14-1 HUMAN HEREDITY 14-2 HUMAN CHROMOSOMES 14-3 HUMAN MOLECULAR GENETICS CH 14: THE HUMAN GENOME.
GENETICS HEREDITY and CHROMOSOMES. INSTRUCTIONS Please define vocabulary words and answer questions...
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Transcript of GENETICS HEREDITY and CHROMOSOMES. INSTRUCTIONS Please define vocabulary words and answer questions...
VOCABULARY
• Chromosome Gene• Allele Gamete• Dominant Recessive• Homozygous Heterozygous• Genotype Phenotype• Karyotype Mutation• Sex chromosomes Autosomes• XX , XY
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) (yellow)
(long) (short)
(long) (short)
1. Green feathers, long beak 2. Green feathers, short beak
3. Green feathers, long beak 4. Yellow feathers, short beak
QUESTIONS!
• 4. What is the percentage of short beaked offspring?
• 5. Is there a single trait 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
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.