GENETICS

HEREDITY and CHROMOSOMES

CHROMOSOMES

• Contain genetic information for organism

• Made of DNA

GENES

• Encode for traits of an organism

• Alternate form of a gene is an allele

• You have 2 alleles for each trait- one from your mother and one from your father

ALLELES

• Alleles can be dominant or recessive.

• Your genotype includes all of the alleles that you carry.

• Your phenotype

is the visible

evidence of your

alleles.

Ex: EYE COLOR

• Brown eyes are dominant over lighter colored eyes.

• In order for brown eyed parents to have a blue eyed child, they both need to carry the recessive allele for blue eyes.

Dominant vs. Recessive

• Dominant alleles are expressed in the organism’s phenotype.

• Recessive alleles are only expressed in the organism’s phenotype if there are two copies of the recessive allele.

PUNNETT SQUARESMonohybrid Cross (One Trait)

• You are given the genotype of the male and the female of a species. You should be able to predict likely phenotypes and genotypes of the offspring.

• Example: Fur color of mice– T-dominant tan– t-recessive white– Female Tt, Male Tt

• Genotypes: What are the allele combinations?TT,Tt,Tt,tt

What is the genotype ratio?1:2:1

Phenotypes: Whatare the colors ofthe mice?Tan, white

What is the phenotype ratio?3:1

YOUR TURN!

• B-dominant gray cheeks

• b-recessive pink cheeks

• 1. What are the

genotypes?

• 2. What are the

phenotypes?

HOMOZYGOUS VS. HETEROZYGOUS

To be homozygous for 2 alleles

means: 2 copies of the

same allele.

Homozygous dominant:

2 copies of dominant allele.

Homozygous recessive:

2 copies of recessive allele.

• To be heterozygous for a trait:One copy of the dominant allele,and one copy of the recessive one.The organism willdisplay dominant traits, but stillcarry the recessive.

INTERPRETING GENOTYPES

• Remember-you can interpret the genotype from the description.

• G-dominant green feathers• g-recessive yellow feathers• L-dominant long beak• l- recessive short beak• Given: ggLl(female) X Ggll(male)• 3. What are the phenotypes of the parents?

PREDICTING OFFSPRING in DIHYBRID CROSSES

• Separate traits into separate Punnett squares: GgLl(female)X Ggll(male)

G g

G

g

MOM

DAD

Gg Gg

1 2

3 4

Gg Gg

MOM

DAD

L l

l

l

Ll ll

Ll ll

1 2

3 4(green) (green)

(green) (green)

(long) (short)

(long) (short)

1. Green feathers, long beak 2. Green feathers, short beak

3. Green feathers, long beak 4. Green feathers, short beak

QUESTIONS!

• 4. What is the percentage of short beaked offspring?

• 5. What trait is visible in all offspring?

• 6. Can you ever have a recessive phenotype when both of the parents have a dominant allele for the trait?

• Using the following information, create a genotype for the male and female birds:

• 7.Homozygous dominant color, and heterozygous beak (female)

• 8.Heterozygous color, and homozygous recessive beak (male)

WHERE DO THE ALLELES COME FROM?

• Gametes-sex cells with half the amount of genetic information.

• In animals, the male sex cell is the sperm and the female is the egg.

KARYOTYPES

• Karyotypes are a map of the chromosomes of an individual.

• This is a karyotype of a male human.• Note that thereare 23 pairs ofchromosomes.• The last pair are the sex chromosomes, and for a male, they are XY.

• Note that this is the karyotype of a female.

• There are 23 pairs of chromosomes, the last pair being XX, a genetic female.

• There are 22 pairs of chromosomes that encode for every trait that the organism will possess, but only 1 pair that indicates the sex of the organism.

• These chromosomes encode for autosomes, (body cells).

• You might also see them

referred to as somatic cells.

GENETIC DISORDERS

• Some genetic disorders are a result of extra chromosomes being present, or deletion of some chromosomes.

• Extra chromosome at the

• 21st= Down Syndrome

• Turner Syndrome is a result of only one X chromosome.

MUTATIONS

• Mutations occur as a result of a change in a protein sequence.

• Some mutations are deleterious, and some are fatal, but some are not.

• Changes in the protein sequence can occur in various ways. Some examples are:

• Deletion-where one base is missing– Ex: ATTGCGAAA ATGCGAAA

• Insertion-where an extra base is added– Ex: ATTGCGAAA ATTGCGAAGA

• All mutations can alter the amino acids in a proteinsequence, thus possiblychanging the protein produced.

• The only mutations that can be passed to offspring are the mutations that occur in the gametes. (Sex cells)

PRACTICE QUESTIONS

• 1. Overexposure to ultraviolet light causes mutations in the DNA of skin cells. The mutated DNA has no effect on offspring because:– A. Changes in skin cell DNA are homozygous

recessive.– B. Mutations must occur within the RNA codons.– C. Offspring reject parental skin cells.– D. Only changes to gamete DNA can be inherited.

• 2. Mutations in DNA molecules occur when:– A. Replication of DNA is exact.– B. A DNA enzyme attaches to an RNA codon.– C. RNA codons are replaced by DNA

nucleotides.– D. A change occurs in a DNA nucleotide

base.

VOCABULARY

• Chromosome Gene• Allele Gamete• Dominant Recessive• Homozygous Heterozygous• Genotype Phenotype• Karyotype Mutation• Sex chromosomes Autosomes• XX , XY

Answers to questions:

• 1. Bb, Bb, Bb, Bb• 2. Gray cheeks• 3.Female-yellow feathers, long beak

– Male- green feathers, short beak• 4. 50%• 5.Green feathers• 6.No• 7.GGLl (female)• 8. Ggll (male)• Practice questions 1 &2- Both are D

TEACHER NOTES

• Begin with BrainPop- Cellular Life and Genetics; Genetics, Heredity, Genetic Mutations.

• Have students take notes on material, as it is heavily tested on TAKS.

• Have students answer embedded questions as you go along.

• Have students make a vocabulary page with words, definitions and illustrations of those definitions to turn in for extra credit in their science class!