Chapter 16

Question 1

how does inheritance work?

Answer 1

• inheritance: traits passed parents to the offspring
• Pre-Mendel, blending inheritance was assumed
• blue-eyed parent X green-eyed parent -> gray-eyed child
• OR if one was “stronger”, child would have traits of that parent

Question 2

inheritance

Answer 2

• we now know that blending inheritance is WRONG
• Mendel- mid 1800s
• conducted experiments, collected data, and used statistics to help explain the results
• he figured out what occurred in the black box

Question 3

Garden Pea, Pisum sativum

Answer 3

• why did Mendel study peas?
• Reason 1- many readily apparent traits
• either/ or inheritance
• either tall OR short, smooth OR wrinkled
• Reason 2- normally self-fertilizing
• true breeding lines exhibit the same traits
• Reason 3- easy to use
• cross-fertilization or hybridization

Question 4

Genotype

Answer 4

• genetic (allele) composition of individual
• TT and tt- homozygous
• Tt- heterozygous
• each letter represents one gene on one chromosome
• each pair of letters represents the two copies of a gene on both homologous chromosomes

Question 5

Phenotype

Answer 5

• characteristics that are the result of gene expression
• TT or Tt are tall
• tt are dwarf

Question 6

single-factor cross

Answer 6

• experimenter follows the variants of only 1 trait

- monohybrid

Question 7

P generation

Answer 7

-true-breeding parents

Question 8

F1 generation

Answer 8

• offspring of P cross

- monohybrids- if parents differ in 1 trait

Question 9

F2 generation

Answer 9

-F1 self-fertilizes

Question 10

Traits are dominant and recessive (mendels 3 ideas)

Answer 10

• dominant- displayed in hybrids

- recessive- masked by dominant

Question 11

Genes and alleles (mendels 3 ideas)

Answer 11

• particulate mechanism of inheritance
• “unit factors” (aka genes)
• every individual has two genes for a character
• gene has 2 variants forms, or alleles

Question 12

segregation of alleles (mendels 3 ideas)

Answer 12

-two copies of a gene carried by an F1 plant segregate (separate) from each other, so that each sperm or egg carries only one allele
0F2 traits follow approximately 3:1 ratio

Question 13

Mendels law of segregation

Answer 13

• two copies of a gene segregate from each other during the transmission from parent to offspring
• during sexual reproduction, homologues replicate and pair
• the pairs segregate (Meiosis I)
• one cell has 2 copies of T-> TT
• one cell has 2 copies of t-> tt
• sister chromatids separate (Meiosis II)
• 2 gametes with T and 2 gametes with t

Question 14

testcross

Answer 14

• dominant phenotype; genotype could be TT or Tt
• multiple by
• recessive phenotype; genotype must be tt
• to determine the genotype of a parent with a dominant phenotype, examine genotypes of offspring when cross with a recessive phenotype

Question 15

law of independent assortment

Answer 15

• alleles of different genes assort independently of each other during gamete formation
• each trait sorts itself independently of the others
• not always he case- if genes are on the same chromosome

Question 16

chromosome theory of inheritance

Answer 16

1. chromosomes contain the genetic material
2. chromosomes are replicated and passed from parent to offspring (cells or kids)
   - each chromosome retains its individuality during cell division and gamete formation
3. each diploid cell contains two sets of chromosomes, which are found in homologous pairs
   - one inherited from mom and one from dad
   - each chromosome of the the set carries a full complement of the same genes
4. during meiosis, one of each chromosome pair segregates randomly into the gamete nucleus
5. gametes are haploid cells that combine to form a diploid cell during fertilization
   - each gamete transmits one set of chromosomes to the offspring

Question 17

Pedigree analysis

Answer 17

• trait analyzed over multiple generations
• medical pedigrees can be helpful for genetic disorders
• provide a family history
• help establish probabilities for future inheritance
• help determine whether condition is
• dominant or recessive
• X-linked or autosomal

Question 18

Cystic fibrosis (pedigree analysis)

Answer 18

• autosomal recessive traint
• approximately 3% of Americans with European descent are heterozygous carries of the recessive CF allele and phenotypically normal
• genotype Cc
• individuals who are homozygous recessive exhibit disease systems
• genotype?
• 2 unaffected individuals CAN HAVE an affected child!
• what is the probability?

Question 19

autosomal dominant disease pedigree- HD

Answer 19

• autosomal dominant usually seen in every generation

- every affected individual has on affected parent

Question 20

X-linked inheritance

Answer 20

• genes found on the X but not the Y are X-linked
• sex-linked genes: on one sex chromosome but not the other
• in humans X is larger, carries more gene
• 1,500 vs 70 genes
• males are hemizygous for X-linked genes

Question 21

X-linked inheritance- Color blindness

Answer 21

• affects more males than females
• 8% of the male population has some degree of colorblindness
• 0.5% of the female population has some degree of colorblindness
• females are “protected”

Question 22

sex-ratio dependent sex determination

Answer 22

• in some fish, sex is controlled dominance heiarchy
• clownfish are all born male
• a dominant male will turn female when the current female of the group dies

Question 23

mendelian inheritance- variations

Answer 23

• inheritance pattern of genes that segregate and assort independently
• simple Mendelian inheritance- one trait is completely dominant over the other
• phenotypic ratios are predictable via Mendels laws
• occurs because dominant gene is enough for functionality

Question 24

incomplete dominance

Answer 24

• heterozygote displays intermediate trait

- why is this not “blending”

Question 25

Phenylketonuria (incomplete dominance)

Answer 25

- autosomal recessive metabolic disorder | - cannot break down phenyalanine

Question 26

homozygotes (incomplete dominance)

Answer 26

-mental impairment and seizures

Question 27

heterozygotes (incomplete dominance)

Answer 27

- do not exhibit symptoms | - but 2x amount of phenylalanine in blood

Question 28

codominance

Answer 28

more than two alleles expressed

Question 29

Human blood type (codominance)

Answer 29

- human blood types; A, B, AB and O - determined by antigens on the surface of RBC - antigens are glycoproteins; used for cell-cell recognition - coded for single gene on chromosome 9 - each individual has 2 alleles of gene that codes for antigens - can be identical or non-identical - 3 alleles of this gene exist in the population - "I^A" allele-> "A" antigen - "I^B" allele -> "B" antigen - "O" allele -> no antigen encoded

Question 30

determining blood type

Answer 30

- body attacks cells with foreign antigens with antibodies - individuals with blood type A will not recognized by bodies with blood type B or vice versa - results in rejection of blood transfusion - O is universal blood donor (has no antigens)

Question 31

pleiotropy

Answer 31

- genes can exhibit this | - affects multiple trait

Question 32

role of environment

Answer 32

- expression of genes is determined by the environment | - genetically identical plants- different heights in different temps

Question 33

gene-environment interactions

Answer 33

- gene expression can vary depending on environment - example: hydrangeas - clones express different colors based on soil conditions

Question 34

Phenotypic plasticity

Answer 34

the ability of an individual to alter genetic expression in response to the environment

Question 35

Role of environment; human example

Answer 35

- Phenylkaptonurians can develop normally if given a diet free of phenylalanine - if their diet contains phenylalanine, they develop mental impairments, underdeveloped teeth and more