Chapter 17 Flashcards
1
Q
Polygenic traits
A
- influenced by many genes
- each with small, additive effect
- interactive
- example: human height involves multiple genes -> growth hormones, cell division, metabolism etc.
2
Q
epistasis
A
- one gene alters the phenotypic expression of a 2nd gene
- often due to 2 or more different proteins involved in a single cellular function
3
Q
epistasis example- lab skin & fur color
A
- B locus- color of melanin pigment (B=black, b= brown)
- E locus is epistatic to the B locus: prevents complete deposition of already-made pigment, but does not affect deposition in skin
4
Q
discrete traits or discontinuous
A
- clearly defined
- purple or white flowers, red or white eyes
5
Q
Continuous or quantitative
A
- majority of traits
- heigh, skin color, number of apples on a tree
- Polygenic- multiple genes contribute to phenotype
- environment also plays a role
6
Q
independent assortment
A
assumes genes are inherited independently of each other
7
Q
non-independent assortment
A
- genes on same piece of DNA are “linked”
- tend to be inherited together
- do not follow the law of independent assortment
- linkage- when 2 genes are close on the same chromosome, they tend to be transmitted as a unit
8
Q
non-independent assortment- fly example
A
- morgan mated a homozygous wild-type female for body color and wing shape to a homozygous mutant male
- female was gray body with straight wings (b+b+c+c+)
- male was black with curly wings (bbcc)
- mated F1 female with fly homozygous recessive for both traits (testcross) to produce F2
- nonrecombinants or parental types- offspring’s traits have not changed from parental generations
- recombinants or nonparental types- different combination of traits from parental generation
9
Q
Morgan’s steps; non-independent assortment
A
- when different genes are located on the same chromosome:
- traits determined by those genes are most likely to be inherited together - due to crossing over during meiosis:
- homologous chromosomes can exchange pieces of chromosomes and create new combinations of alleles - the likelihood of crossing over depends on:
- the distance between two genes
- 2 genes farther apart ->more likely to cross over
- 2 genes close together -> less likely to cross over
10
Q
genetic mapping
A
- if genes are linked, then the frequency that they end up in different offspring is the recombination frequency
- use recombination frequency to determine how closely linked genes are
- the closer they are linked, the lower the recombination frequency
- one can make a chromosome map of the genes
- one map unit is a 1% recombination frequency
11
Q
extranuclear inheritance
A
- what other organelles contain DNA?
- example: leaf pigmentation- maternal inheritance
12
Q
extranuclear inheritance- Mitochondria
A
- example: Neurogenic muscle weakness
- mutations in mito gene that encodes ATP synthase
- abnormalities of NS, eyes and muscles
13
Q
epigenetic inheritance
A
- genetic modification that does not change DNA sequence, effects gene expression
- occurs during egg or sperm formation or early embryonic development
- usually fixed throughout life
- but not necessarily throughout several generations
14
Q
X-inactivation in female mammals
A
- only one X-chromosome active in each somatic cell
- second condensed into Barr body
- methylated, lies along inside of nuclear envelope
- which one is silenced is random
- dosage compensation-inactivation of an X gives equal expression of x-linked genes as seen in males
15
Q
calico cats- X-inactivation example
A
- patchy pattern due to inactivation of one X chromosome in each cell
- X-linked gene for coat color
- orange allele, X0and black allele, X8
- heterozygous X0/X8 female will be calico
- in early development, one of the 2 X chromosomes is randomly inactivated in each somatic cell
- one or the other X is inactivated in different groups of cells, resulting in patches of black and organ fur
