Notes: Genetics

Essential Question: How does genotype determine phenotype?

What are Mendel’s Laws?

A. Law of Segregation

1. During meiosis, the genes that control each trait separate.

2. One gene from each pair is passed to the offspring. Haploids have only 1 of each gene.

3. These genes randomly unite (combine) at fertilization.

B. Law of Independent Assortment

1. The inheritance of one trait is unaffected by the inheritance of another trait.

2. You may get your eye color from mom but hair color from dad.

How are genotype and phenotype related?

Phenotype: physical characteristics or traits

Genotype: genes

How are genotype and phenotype related? Dominant Allele A VERSION OF THE TRAIT THAT IS ALWAYS EXPRESSED.

Represented by CAPITAL LETTER

R, T, D

How are genotype and phenotype related? Recessive Allele A VERSION OF THE TRAIT THAT IS ALWAYS MASKED IF PAIRED WITH A DOMINANT ALLELE.

Represented by LOWERCASE LETTERs

r, t, d

Possible combination of alleles

GENOTYPES:1.Homozygous dominant (ex:

RR, TT, EE)2.Homozygous recessive (ex:

rr, tt, ee)3.Heterozygous (ex: Rr, Tt, Ee)

Heterozygous genotypes always express the dominant trait!

Example 1Brown eyes (B) are dominant over blue

eyes(b) .

What are the 3 possible genotypes?

BB, Bb, bb

What are the phenotypes?

BB-brownBb-brownbb-blue

What are the step involved in solving Punnett squares?

1.Decide on all possible genotypes/phenotypes.

2.Find the genotype of the parents.

3.Do a “Punnett” square to show the possible combinations of genes in the offspring.

Example Genetic Problem

Straight thumb (T) is dominant to hitchhiker’s thumb. If Brenda, who is heterozygous for this trait had children with Jason who is homozygous recessive, what is the chance that their children will be able to hitchhike correctly?

Straight thumb (T) is dominant to hitchhiker’s thumb. If Brenda, who is heterozygous for this trait had children with Jason who is homozygous recessive, what is the chance that their children will be able to hitchhike correctly?

1.What are all possible genotypes/ phenotypes?TT- Straight thumbTt- Straight thumbtt- hitchhiker’s thumb

2. Find the genotype of the parents.

Brenda TtJason tt

Straight thumb (T) is dominant to hitchhiker’s thumb. If Brenda, who is heterozygous for this trait had children with Jason who is homozygous recessive, what is the chance that their children will be able to hitchhike correctly?

3. Do a Punnett square to show the possible combinations of genes in the offspring.

T t

t

t

Tt tt

Tt tt

Straight thumb (T) is dominant to hitchhiker’s thumb. If Brenda, who is heterozygous for this trait had children with Jason who is homozygous recessive, what is the chance that their children will be able to hitchhike correctly?

Mother Tt

Fathertt

Tt tt

Tt tt

Tt- straight thumbTt- hitchhiker’s thumb

2/4= 50%

Straight thumb (T) is dominant to hitchhiker’s thumb. If Brenda, who is heterozygous for this trait had children with Jason who is homozygous recessive, what is the chance that their children will be able to hitchhike correctly?

Example Genetics Problem #2

Having freckles (F) is dominant over not having freckles (f). A woman is heterozygous marries a man who is homozygous recessive. What are the chances of their children having freckles?

Find the genotype of the parents.

Woman FfMan ff

Example Genetics Problem #2

Do a Punnett square to show the possible combinations of genes in the offspring.

F f

f

f

Ff ff

Ff ff

Mother Ff

Fatherff

Example Genetics Problem #2

Ff ff

Ff ff

Ff- freckles ff- no freckles

2/4= 50%

Example Genetics Problem #2

Exit Ticket: 3, 2, 13: In three complete sentences, write three things you learned about in today’s lesson.

2: List two things you found interesting.

1: Draw an Emoji that best describes how comfortable you feel with the material OR write one question you still have.