Chapter 8: Inheritance, Genes, and Chromosomes Flashcards
What is crossing over?
Exchange between non-sister chromatids that produces recombination between DNA molecules
What is independent assortment?
Haploid sets of chromosomes inherited from parents, mixed by segregation of homologs during Meiosis
What is a chiasma?
The point of contact or physical link between two (non-sister) chromatids belonging to homologous chromosomes
What is produced as a result of crossing over?
Recombinant DNA/chromatids
What do haploid gametes represent?
parental chromosomes
How do you calculate the number of possible combinations of chromosomes in cells?
2^n where n is the number of homologous pairs
In what phase of meiosis does crossing over occur?
Prophase 1
In what phase of meiosis does independent assortment occur?
Anaphase 1
Does crossing over and independent assortment occur during Meiosis 1 or Meiosis 2?
Meosis 1
Mendel’s first law
Law of segregation: The two alleles of a gene separate and are transmitted individually and equally to gametes
Outcome of the law of segregation
50% gametes with allele 1 and 50% of gametes with allele 2
Pure-breeding lines
same phenotype occurs each time individuals are crossed within the line
Inference
the lines are homozygous containing the same allele on both homologous chromosomes
What is the P generation?
parental generation
What is are F generations?
Offspring, and their offspring, and so on
Homozygote
Has an identical genotype (ex. AA)
Heterozygote
has a varied genotype (ex. Aa)
What is a test cross?
Take a organism that has a genome you don’t know, and cross it with a homozygotes to find out what the mystery genome is
Locus
A particular site on a chromosome
What is a gene?
a sequence within a DNA molecule that resides at a locus; the function of the gene influences characteristics of an organism; its a protien
T/F different aleles segregate equally to gametes during meiosis according to the law of segregation
T; because genes are shared by homologous chromosomes
What mechanism is responsible for the law of segregation?
The transmission of chromosome pairs through meiosis
Mendel’s second law
The law of independent assortment; alleles of different genes assort independently during gamete formation
Outcome of independent assortment
25% of gametes with each combination of alleles at two loci
What is the probability for each phenotype in a dihybrid cross?
Both dominant 9/16
Half dominant 3/16
Other half is dominant 3/16
Both recessive 1/16
Alleles of genes on different chromosomes _______ during gamete formation
assort independently
Linkage
alleles of separate loci are transmitted together to offspring
What are parental types?
look like the parent (phenotype) but doesn’t necessarily have the same genotype
What does Mendel’s 2nd Law
recombinant types
Each chiasma involves ____ non-sister chromatids of the tetrad. What does it produce?
2
2 recombinant chromatids
What does one crossover produce?
two recombinant gametes and two parental gametes
How can you tell if there is linkage?
There is an excess of parentals over recomninants
How do you calculate recombinant frequency?
of recombinants / # of total offspring
Genes that are closer together are going to have _____ recombinants
fewer
What is the maximal recombinant frequency
0.5
When is there no linkage
They are either on the same chromosome or so far apart on two different chromosomes that there is always a crossover
Is absolute linkage rare? Why or why not?
Rare; even alleles of different loci that are very close on the same chromosomes are sometimes recombined by crossing over
What are the three key principles of genome-wide inheritance
segregation, independent assortment, recombination
What forms a linkage group
All of the loci on a chromosome
What is the distance between genes? What is it called?
Called a map unit or centimorgan (cM)
100 x recombinant frequency
What is the genetic size of all autosomes
3,590 cM
What is the genetic size of an X chromosome
195 cM
If given distances, and trying to find the recombinant frequency
find the different of the distances and divide by 100
When is recombinant frequency 0.5?
If recomb frequency = 0.5 or is greater than 0.5
What are sex chromosomes? What are autosomes?
Sex chromosomes are the genes with primary control of sexual development and are present on the sex chromosomes
Autosomes are all other chromosomes
Home many chromosomes are in the human karyotype
23 pairs (2n = 46)
22 pairs autosomes, a single pair of sex chromosomes
Which gender is which genotype
Female: XX
Male: XY
How many gametes produced by males determine the sex of a zygote
2
What is the SRY gene?
sex-determining region on the Y; encodes a protein that initiates male development
What do sex chromosome abnormalities result from?
nondisjunction in meiosis; pair of homologous chromosomes fail to separate in Meiosis 1 or a pair of sister chromatids fail to separate in Meiosis 2
What is the genotype of Turner syndrome? Klinefelter syndrome?
Turner: X, only one sex chromosome
Klinefelter syndrome: XXY, affects males are results I sterility and overlong limbs
Genes on sex chromosomes exhibit _____
sex-linked inhertiance
Which carries more genes X or Y
X cares many, Y carries a few
T/F males have two copies of genes of the X
False; males have only one copy of the genes of the X (hemizygous) and express the phenotype of that allele
What are traits of X-linked recessive phenotypes
appear much more often in males than females; heterozygous females are carriers; phenotype can skip a generation if it passes from a male to his daughter and then grandson
Drosophila melanogaster Karyotype
4 pairs of homologous chromosomes (2n = 8)
3 pairs of autosomes (2 large, 1 small)
single pair of sex chromosomes
Drosophila in general
Female has XX
Male has XY
Males produce two types of gametes that determine the sex of the zygote
In Drosophila, the number of X chromosomes establishes _________
alternative pathways of female (2X) or male (1X) development
What do sex chromosomes contain?
the gene(s) that determine sex and exhibit unique patterns of inheritance
Bees Sex Determination Mechanism
males are haploid, females are diploid
Fruit Flies Sex Determination Mechanism
Fly is female if the ratio of X chromosomes to sets of autosomes is 1 or more
Birds Sex Determination Mechanism
Males ZZ (homogametic), females WZ (heterogametic)
Mammals Sex Determination Mechanism
Males XY (heterogametic)
Females XX (homogametic)
What is the first clue of sex linkage
Reciprocal Crosses
What is hemizygous expression?
When there is only one copy of genes, which is the phenotype
What is complete dominance
The heterozygotes appear similar to one of the homozygotes; used to define dominant and recessive allele
Why is one allele dominant over the other
It encodes a functional protein so that the one allele of the heterozygote is sufficient to produce the same phenotype as the two functional alleles
When one gene is dominant over another, what does the recessive phenotype result from?
The absence of the functional protien that encodes the dominant gene
With complete dominance, what is the ration of dominant offspring to recessive offspring?
Near 3
Incomplete dominance
When heterozygotes have an intermediate phenotype that doesn’t take on the traits of the dominant or recessive phenotype
With incomplete dominance, what does a monohybrid cross produce?
Produces a 1:2:1 ratio of phenotypes in F2, so that each genotype has a distinct phenotype (the intermediate phenotype)
What are the alleles for coat color in rabbits? Which are dominant and recessive?
C (dominant) –> dark gray
c^chd –> chinchilla
c^h –> point restricted
c (recessive)–> albino
What is co-dominance?
Phenotypes of both alleles appear in the heterozygote
Physical characteristics reflect underlying _______ such as ________ within biochemical pathways
cellular functions
enzymatic activity
Epistasis
The phenotype expression of one gene is influenced by the genotype of another gene
What indicates epistasis
modified dihybrid phenotype ratio
Probability of two independent events happing together
multiply
Probability of an event occurring in two mutually exclusive ways
add
For independently assorting loci, each locus can be treated as ___________ within the dihybrid cross
independent events
Some traits of single gene disorders. What are the two types?
Rare, caused by a mutant allele of a single gene, results in a change in phenotype; recessive disorders and dominant disorders
How many alleles need to be mutant in recessive disorders? What are a few examples?
Both alleles
Albinism, cystic fibrosis, PKU, sickle cell anemia, Tay-Sachs, muscular dystrophy
How many alleles need to be mutant in dominant disorders? What are a few examples?
One allele
Huntington disease, achondroplasia
General rule for dominant inheritance
affected individuals always have an affected parent
General rule for recessive inheritance
Affected individuals can appear in families, even when both parents are unaffected
Albinism
A = tyrosinase
a = mutant
aa does not make active tyrosinase & produces no melanin, resulting in albino phenotype
Achondroplasia
A dominant form of dwarfism
d encodes growth factor receptor that functions as a negative regulator of long bone growth
D produces too much of the receptor and causes reduced growth of long bones
What is the response of each genotype of achondroplasia
Dd = dwarfism
dd = normal stature
DD = lethal
Describe Mendelian traits
single gene affecting discrete phenotypic differences. phenotypes vary continuously over a range due to the action of multiple different genes and the environment
Examples of Mendelian traits
height, weight, skin pigment
