Introduction to Genetics

Introduction to Genetics

Chapter 6

Mr. Scott

Meiosis

Meiosis

Chromosome number

Fruit fly

Body cell – 8 Chromosomes

4 from mom

4 from dad

Homologous chromosomes –

Meiosis

Diploid – cell that has ______of homologous chromosomes

2N



Haploid – cells that have just ______of chromosomes

1 N



Meiosis

Phases of meiosis

A process of reduction and division in which the number or chromosomes per cell is cut in half through the separation of homologous chromosome in a diploid cell

Meiosis

Meiosis I



Each chromosome lines up with its corresponding homologous chromosome making a tetrad

They exchange genetic information called crossing-over

______separate and form two new cells with different chromosome and alleles

Meiosis

Meiosis II

______divide

Neither cell makes a copy of the chromosomes

All four new cells have ______of chromosomes

Meiosis

Gamete formation

Haploid cells





Meiosis

Mitosis vs. Meiosis

Mitosis results in two genetically ______cells

Meiosis results in four genetically ______cells

The Work of Gregor Mendel

The work of Gregor Mendel

Austrian monk who is the ______

Genetics – the scientific study of heredity

The Work of Gregor Mendel

Fertilization – when male and female reproductive cells join

Male –

Female –

Gamete –

Seed – fertilized egg or new cell (zygote)

The Work of Gregor Mendel

True-breeding – if they were allowed to self-breed they would have ______

Self-breeding – Sperm and egg from the same flower fertilize

 Experiment

Cross-pollination



The Work of Gregor Mendel

 Genes and Dominance

Traits______

 Seed color

 Plant height

Parental generation (P) – Original pair of plants

Filial generation (F1) – offspring, progeny

Hybrids – offspring of crosses between parents with different traits

The Work of Gregor Mendel

Genes –

Alleles –

The Work of Gregor Mendel

Principle of Dominance – some alleles are ______and other are ______

Dominant traits will always show over recessive traits

The Work of Gregor Mendel

Segregation

 F1 generation self-pollinated

 F1 X F1 = F2

 F1 Cross

 ¼ of the F2 plants now show the recessive traits

The Work of Gregor Mendel

Explaining the F1 Cross

When each F1 plant flowers and produces gametes, the two alleles ______from each other so that each gamete carries only a ______of each gene.

Therefore, each F1 plant produces two types of gametes—those with the allele for tallness and those with the allele for shortness.

Segregation -

Probability and Punnett Square

Probability and Punnett Square

 Probability in Genetics

Probability –

 Coin flip

 ½ or 50 %

 3 Coin flips

 ½ X ½ X ½ = 1/8

Past outcomes do not affect future ones

Probability and Punnett Square



A diagram showing the gene combinations that might result from a genetic cross

Letters represent each allele

Top and left letters are the parents genes

The four boxes show each possible gene combination

Probability and Punnett Square

GG, Gg, gg are all of the possible combinations of genes

GG means ______

gg means ______

Gg means ______

Probability and Punnett Square

Phenotype



Tall or short

Purple or white

Genotype



GG, Gg, or gg

Probability and Punnett Square

Probability and segregation

Each parent only ______to each offspring

Probability and Punnett Square

Probabilities predict averages, not exact outcomes

Probability is more accurate when you have ______

Exploring Mendelian Genetics

Two-factor cross : F1

Crossing true-breeding organisms does not answer this question

They do produce hybrid offspring used for the next test

 RrYy

Exploring Mendelian Genetics

Two-factor cross : F2

 9:3:3:1 ratio

Exploring Mendelian Genetics

 Exploring Mendelian Genetics



The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes.

Independent assortment helps account for the ______in plants, animals, and other organisms.

Exploring Mendelian Genetics

Mendel’s Principles

The inheritance of biological characteristics is determined by individual units known as genes. Genes are passed from parents to their offspring.

In cases in which two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive.

In most sexually reproducing organisms, each adult has two copies of each gene—one from each parent. These genes are segregated from each other when gametes are formed.

The alleles for different genes usually segregate independently of one another.

Exploring Mendelian Genetics

Beyond dominant and recessive alleles

Incomplete dominance –

Exploring Mendelian Genetics

Codominance –

Exploring Mendelian Genetics

Multiple allele – more than two alleles

Polygenic trait



Exploring Mendelian Genetics

Mendel’s Principles

Apply to animals as well as plants

More importantly to humans

Exploring Mendelian Genetics

Genetics and the Environment

Environment affects how genes are displayed