Genes Are the Basic Unit of Inheritance by Which Characteristics Are Passed on from One

Genes

▪Genes are the basic unit of inheritance by which characteristics are passed on from one generation to another.

▪DNA-Deoxyribonucleic acid, contains instructions in the form of 4 chemicals which act as code letters.

▪DNA forms double helix and has 4 bases- Adenine (A), guanine(G), cytosine(C), thymine(T). They form pairs, A and T; G and C.

▪Chromosomes – long strands of DNA. In each cell, the nucleus has 46 chromosomes, 23 from mother and 23 from father.

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▪Trait- Physical characteristics that are passed down / inherited from one generation to next, genes code for specific traits.

▪Alleles- Different versions of the same gene.

▪Allele-One version of the pair of genes that appear at a particular location on a particular chromosome and control the same characteristics like eye color.

▪Organisms typically have two alleles for a trait

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▪Dominant- Allele that shows trait whenever it is present.

▪Recessive- Weaker gene, Eg: Eye color, brown from mom, blue from dad.

▪Homozygous-When Alleles for a characteristic are same, the organism is homozygous for that characteristic.

▪Heterozygous- When the alleles are different for a characteristic, then the organism is heterozygous for that characteristic.

▪Genotype- the information in genes that make up that trait

▪Phenotype-Actual appearance of organism.

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When allele pairs are the same, they arehomozygous. When the alleles of a pair are different, they are heterozygous. Thephenotypeof one trait may be dominant and the other recessive. The dominant allele is expressed and the recessive allele is masked.

Punnett Square

▪B- Brown eyes (Dominant)

▪b-blue eyes (Recessive)

▪BB-Homozygous Dominant; Bb-Heterozygous

▪bb-Homozygous Recessive

Inherited and Acquired Traits

▪Traits are features or visible characteristics

▪Behavior is a way in which living this react or act to its surrounding environment.

▪Inherited trait: Trait received by offspring from parent. Both physical and behavioral characteristics can be inherited. Behavioral trait is also called instinct.

▪Instinct is a behavior that comes naturally without being taught.

▪Acquired trait: Behaviors that are learned or acquired through interaction with environment and life experiences.

Inherited Traits

▪Inherited traits are coded in your DNA and you receive it from your parents. Physical and Behavioral inherited traits (instinct). Because inherited traits are coded in the DNA, they can be passed on to the next generation

Inherited Physical Traits / Inherited Behavior Traits
eye color, hair color, skin color / birds hatching from eggs
tongue rolling / Birds protecting their egg(instinct)
thumb rolling back / Birds flying in groups
Long neck of giraffe / Birds migrating (instinct)
zebra stripes / bears hibernation
Ear shape, fur color,leaf shape

Acquired Traits

▪Acquired traits develop during life (organism is not born with it) .Animals learn these when they interact with environment. It is not in your DNA. It will not be passed on to next generation.

▪Examples -Things you learned (riding a bike, reading, writing), scars from injury,

▪Things that happened to you (short hair, broken bone)

▪Acquired Behavior Traits eg: playing musical instrument, dog learning tricks

▪Inherited Physical TraitAcquired Physical Trait Scar

Inherited Behavior TraitAcquired Behavior Trait

Some are little bit of both

•Animals have the instinct to hunt but must learn hunting skills

•Receive skin color from parents, but amount of time in sun determines tan.

Habitats and Adaptations

▪Anadaptationis a genetic change, or mutation, that makes theorganismbetter able to survive in its newenvironment.

▪Through the process of evolution,organismsretain the strongest traits and features that allow them to breed, find food, and survive in certain habitats.

▪An animal's living place is called its habitat. Most animals are only adapted to live in one or two habitats.

▪Plants are perhaps the most important part of a habitat. For wildlife, plants provide shelter, nesting sites, and a variety of foods . Trees and shrubs help reduce heating and cooling by providing summer shade and protection from winter winds

▪Habitats are places in nature that provide food, protection from predators and unfavorable weather, and a home in which to raise young.

▪Habitats are characterized most often by climate and location. They can range from warm, moist areas to cold polar areas such as the Arctic.

▪Eg of habitat: Grassland, desert, forest, mountains, Artic and Antarctic, freshwater, ocean, coral reef

▪Eg of home: hive, nest, burrow, hole, den, shell, web, trees, aquatic plants (duckweed, water lilies)

Adaptation through body parts or Behavior to find food, adapt to variations in climate and protection from enemies

Picture taken from National Geographic Animal Encyclopedia

Adaptation through body parts or Behavior to find food, adapt to variations in climate and protection from enemies

Picture taken from National Geographic Animal Encyclopedia

Animal adaptations for existence in varied habitats

Picture taken from National Geographic Animal Encyclopedia

Animal adaptations for existence in varied habitats

Picture taken from National Geographic Animal Encyclopedia

Eagle

▪Well adapted eyesight for hunting

▪eyes shadowed by bony ridge that keep sun from glaring.

▪Feet has sharp talons. Bottom of feet have bumps that increase traction and can hold onto prey.

▪Beak tapers down to hook to tear into flesh of prey.

▪Digestive system, regurgitates part of undigested animal like bones.

▪Flight- large wingspan. Soaring keeps from wasting energy.

Camel

▪Lives in desert where winds blow sand and extreme temperature variations and scarcity of water.

▪Has long eyelashes, closed nostrils and ears covered with hair to prevent sand from going into eyes, nose and ears.

▪Can drink 36 gallons of water at a time and can survive without water for a week.

▪Body temperature changes with environment so it doesn’t lose water through sweating.

▪Stores fat in hump to be converted as energy, can live without food for month

▪Color blends with surrounding

▪Wide feet to walk across desert sand

Polar Bear

▪Polar bears are strong swimmers. They can swim for several hours at a time over long distances. A polar bear's front paws propel them through the water dog-paddle style

▪A polar bear's nostrils close when under water

▪excellent insulation keeps a polar bear warmthrough a thick layer of fur, a tough hide, and an insulating fat layer

▪White fur provides insulation from cold and camouflage

▪Small ears to reduce heat loss

Chameleon

▪Chameleons can move their eyes independently and 360 degrees to see all around them, to protect them from predators

▪Tail helps them hang from trees

▪Changes in skin color to communicate with other chameleons and regulate body temperature.

▪Can extend tongue out by a foot to catch insects

References

▪National Geographic Animal Encyclopedia

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Punnett Squares

▪Gregor Mendel, a priest was very curious about how traits were passed from one generation to another. He experimented with peas (29,000 plants!) for seven years and used mathematical principles to figure it all out.

▪Mendel determined that traits aren't blended but are instead passed on, intact, from parent to child. He found that everyone got two genes for each trait — one from the mom and one from the dad.

▪He also concluded that some traits are dominant and some are recessive.

▪Mendel took a tall pea plant and crossed it with a short one. He expected medium pea plants, but what he got was all tall pea plants! Mendel then crossed these tall babies (he called them the F1 generation) and he got three tall plants and one short plant.

▪Dominant traits- always shows up even if there a different gene for the same trait

▪Recessive trait –trait that doesn’t show up if there is a dominant gene.

▪Example: if you have a gene for attached ear lobe and a gene for detached ear lobe, you will have attached ear lobes as it is a dominant trait.

▪Phenotype -The way you look on the outside

▪Genotype- the way you really are deep down in your genes.Homozygous-When Alleles for a characteristic are same, the organism is homozygous for that characteristic.

▪Heterozygous- When the alleles are different for a characteristic, then the organism is heterozygous for that characteristic.

•Alleles- Different versions of the same gene.

•Allele-One version of the pair of genes that appear at a particular location on a particular chromosome and control the same characteristics like eye color.

Punnett Square

Identify the trait that is to be studied
Assign a letter to represent the trait. Don’t use letters where the capital and the lowercase look similar, like S,O and W.
Then draw the square. Since you are only investigating one trait and each trait has two genes, then the Punnett square should have four boxes.
Place each parent's genes on the outside of each square
B B

Bb / Bb
Bb / Bb

B- Dominant Brown eye color

b- recessive blue eye color

▪monohybrid crossis used to determine the dominance relationship between two alleles. Thecrossbegins with the parental (P1 or P) generation. One parent is homozygous for one allele, and the other parent is homozygous for the other allele. The offspring make up the first filial (F1) generation.

▪Cross that looks at one trait

▪Originally, we know one parent is tall and its genotype is TT (remember, we're talking about what you look like in your genes, and you have two alleles, or gene options, for each trait), so we put those letters on one side of the square. The other parent is short and its genotype is tt, so we put those letters on the other side. Every baby plant gets an allele from each of them.

▪All the pea kids are all tall because, in peas, tall is dominant.

▪Genotype-heterozygous (half tall and half short)

▪Phenotype- Tall (short trait is hidden)

F1 Generation

T / T
t / Tt / Tt
t / Tt / Tt

▪Crossing the F1 generation tall plants (Tt) will give F2 generation plants consisting of 3 tall plants and 1 short plant.

▪The short trait which was missing in F1 generation appears in F2 generation. The trait did not disappear, it was hidden as it was a recessive trait.

▪Genotype (1:2:1)

–1 Homozygous dominant

–2 Heterozygous

–1 Homozygous recessive

▪Phenotype (3:1)

–3 tall, 1 short

F2 Generation

T / t
T / TT / Tt
t / Tt / tt
P / P
w / Pw / Pw
w / Pw / Pw

Pea plant with purple flowers (P) and another Pea plant with white flowers (w)
Purple color(P)-Dominant gene
White color(w)-recessive gene
F1 generation will have all purple flowers as purple is the dominant gene.
Genotype-heterozygous; Phenotype-Purple
F2 generation ¾ will have purple flowers and the ¼ will have white flowers (which skipped a generation).
Genotype (1:2:1)

1 Homozygous dominant
2 Heterozygous
1 Homozygous recessive

Phenotype (3:1)
3 purple, 1 white

F1 Generation

P / w
P / PP / Pw
w / Pw / ww

F2 Generation

Practice questions

In pea plants, spherical seeds (S) are dominant to dented seeds (s). In a genetic cross of two plants that are heterozygous for the seed shape trait, what fraction of the offspring should have spherical seeds?

A.None

B.1/4

C.1/2

D.3/4

E.All

A genetic cross between two F1-hybrid pea plants having yellow seeds will yield what percent green-seeded plants in the F2 generation? Yellow seeds are dominant to green.

A.0%

B.25%

C.50%

D.75%

E.100%

References

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Common Human Inheritable Traits and Pattern of Inheritance

▪These are some of the common dominant and recessive traits in humans that can be easily observed in people around you.You have two genes for them. One inherited from your father and one from your mother. The way that a physical trait is expressed, and hence the way you look is a result of either a combination of dominant genes, a dominant and a recessive gene or two recessive genes.

▪hairline shape-v shaped (widows peak) or straight

▪earlobe attachment-free ear lobes, attached ear lobes

▪tongue rolling

▪handedness

▪cleft chin, Dimples, freckles,

▪naturally curly hair

▪hand clasping

▪colorblindness

Hairline

One example of a dominantly inherited trait is the presence of a widow’s peak(v shaped) at hairline. Straight hairline is recessive trait.
(W) is the dominant allele, and (w) represent the recessive allele. An individual with a (WW) or (Ww) genotype will have a V-shaped peak at the hairline. Only ww individuals will have a straight hairline.

Genotype (1:2:1)

- 1 Homozygous dominant

- 2 Heterozygous

- 1 Homozygous recessive

Phenotype (3:1)

- 3 V shaped hairline,1 straight hairline

Earlobes

▪Free ear lobe is dominant (E). Attached earlobe is recessive (e).

▪(E) is the dominant allele, and (e) represent the recessive allele. An individual with a (EE) or (Ee) genotype will have free earlobes.. Only (ee) individuals will have attached earlobes.

Genotype (1:2:1)

- 1 Homozygous dominant

- 2 Heterozygous

- 1 Homozygous recessive

Phenotype (3:1)

- 3 free earlobes, 1 attached

Tongue Rolling

▪One example of a dominantly inherited trait is the presence of the ability to roll your tongue. The tongue-rolling version is dominant over the one that doesn't let you roll your tongue

▪(T) is the dominant allele, and (t) represent the recessive allele. An individual with a (TT) or (Tt) genotype can roll their tongue. Only tt individuals cannot roll the tongue.

▪There are many examples of parents who can't roll their tongues having tongue-rolling children.Tongue rolling is not a simple dominant trait.

Handedness

▪Like many complex traits, handedness does not have a simple pattern of inheritance.

▪Children of left-handed parents are more likely to be left-handed than are children of right-handed parents.

▪However, because the overall chance of being left-handed is relatively low, most children of left-handed parents are right-handed.

▪Many twins have opposite hand preferences.

Cleft Chin, Dimples

▪A cleft chin, also known as a dimpled chin, is a distinctive facial characteristic which is inherited.

▪Dimples can be present on one or both cheeks. The genetics of dimples follows a dominant pattern of inheritance, a child only needs to inherit one dominant gene for dimples to have them.

▪Draw Punnett square for both parents having dimples, father having dimples and mother doesn’t have dimples, both parents not having dimples.

▪Freckles show a dominant inheritance pattern: parents who have freckles tend to have children with freckles.

▪Other genes and the environment influence freckle size, color, and pattern.

Punnet Square to determine Cleft chin heredity

Naturally Curly Hair

▪There are two versions of the hair type gene, curly (C) and straight (s). Hair type is an example of incomplete dominance.

▪If you have one of each version of the gene, you get a mix of the two or wavy hair. So for hair type,CCgives curly,Csgives wavy andssgives straight hair.

Color Blindness

▪Traits that are determined by alleles carried on theX chromosomeare referred to asX-linked. X-linked alleles require a specific notation: Xc (recessive allele) or X+(Dominant allele).

▪ Females will have two X-linked alleles (because females are XX), whereas males will only have one X-linked allele (because males are XY).

▪One example of an X-linked trait is red-green colorblindness.

▪Females that are X+X+or X+Xchave normal color vision,

▪Females that have XcXc are colorblind.

▪Males that are X+Y have normal color vision

▪XcY males are colorblind.

(Xc) -recessive allele that causes colorblindness
(X+)- the normal dominant allele.

Hand Clasping

Most people place their left thumb on top of their right and this happens to be the dominant phenotype.
Right thumb on top of left thumb is recessive.

References

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