Bio Ch. 12
A mother with type A blood and genotype IAi and a father with blood type B and genotype IBi have children who grow up and become regular blood donors. Of the possible children, which genotype would have the least valuable blood to donate?
IAIB
A person with type B blood can receive blood from people with which allele combinations?
IBi
Genes H, T, and Q lie close to each other on the same chromosome, so that independent assortment does not occur. A mother has alleles H T Q on one chromosome and alleles h t q on the other chromosome. The father is homozygous for h t q. What are possible offspring genotype(s)?
hh tt qq Hh Tt Qq hh Tt qq hh tt Qq
which of the following is not a part of mendel's five element model
if an allele is present it will be expressed
an organism's_______ is determined by its _____
phenotype; genotype
phenotype
physical appearance
People with type AB blood have
both type A and type B antigens on their red blood cells.
T.A. Knight (1823)
crossed 2 varieties of garden pea 1st generation resembled only 1 parent strain 2nd generation resembled both
josef kolreuter (1760)
crossed tobacco strains to produce hybrids differed from both parents additional variation observed in 2nd generation offspring contradicts direct transmission
heterozygous
different alleles
F1 generation
first filial generation all f1 plants resembled only 1 parent (dominant gene)
According to Mendel's Principle of Independent Assortment
each pair of alleles segregates independently of the other allele pairs.
mendel's model of inheritance assumes that
each trait is controlled by single gene each gene has 2 alleles there is a clear dominant-recessive relationship between the alleles
the f1 generation of the monohybrid cross purple x white flower pea palnts should
have all purple
when you cross true breeding tall and short tobacco plants you get an F2 that is intermediate in height. When this f1 is self crossed it yields an f2 with a continuous distribution of heights. what's the best explanation for this data?
height is determined by the additive effects of many genes
heredity concepts before the 20th century
heredity occurs within a species traits are transmitted directly from parent to offspring
phenotypes like height, which show a continuous distribution, are usually the result of
the action of multiple genes on a single phenotype
According to Mendel's Principle of Segregation
the two alleles at each gene locus separate during gamete formation.
genotype
total set of alleles an individual contains (AaBbCc)
incomplete dominance
heterozygote is intermediate in phenotype between 2 homozygotes Ex. red flowers + white flowers = pink flowers
if the two genes in the previous question showed complete, linkage, what would you predict for an F2 phenotypic ratio?
1 red tall: 2 pink tall: 1 white short
homozygous
2 of the same allele
the f1 purple and white flower pea plants are allowed to self fertilize. The phenotypic ratio for the F2 should be
3 purple: 1 white
principle of segregation
two alleles for a gene segregate during gamete formation and rejoined at random, one from each parent physical basis for allele segregation is the behavior of chromosomes during meiosis
Japanese four o'clocks that are red and tall are crossed to white short ones, producing an F1 that is pink and tall. If these genes assort independently, and the F1 is self-crossed, what would you predict for the ratio of F2 phenotypes?
3 red: 6 pink tall: 3 white tall: 1 red short: 2 pink short: 1 white short
Consider a diploid cell that contains genes Y, R, and Z on separate chromosomes. How many gamete genotypes are possible if a Yy RR Zz cell undergoes meiosis?
4
The fact that maternal and paternal chromosome pairs line up randomly during metaphase of meiosis supports Mendel's
Law of Independent Assortment
Identify the following exceptions to Mendel's model of inheritance by completing the sentences with the correct terms.
When a single trait is affected by more than one gene locus, this is called polygenic inheritance. When a single gene locus affects more than one trait, this is called pleiotropy. When a single gene locus has more than two possible alleles, this is called multiple alleles. When the phenotype of heterozygotes is intermediate between the homozygotes, this is called incomplete dominance. When the phenotype of heterozygotes shows some aspects of both homozygotes, this is called codominance. When alleles at one gene locus can interfere with the expression of alleles at another gene locus, this is called epistasis
principle of independent assortment
in a dihybrid cross, the alleles of each gene assort independently the segregation of different allele pairs is independent independent alignment of different homologous chromosome pairs during metaphase 1 leads to the independent segregation of different allele pairs
What property distinguished mendel's investigation from previous studies?
mendel quantified his results
What is the probability that a mother with type A blood and genotype IAi and a father with type AB blood will produce a child with AB blood?
0.25
mendel's ratio
1 true breeding dominant plant 2 not true breeding dominant plants 1 true breeding recessive plant
mendel's 5 element model
1. parents transmit genes 2. each individual receives one copy of a gene from each parent 3. not all copies of a gene are identical 4. alleles remain discrete - no blending 5. presence of allele doesn't guarantee expression
mendel's experimental method
1. produce true breeding strains for each trait he was studying 2. cross fertilize true breeding strains having alternate forms of a trait 3. allow the hybrid offspring to self fertilize for several generations and count the number of offspring showing each form of the trait
A and B are independent events. The probability that A will happen is 1/4 and the probability that B will happen is also 1/4. What is the probability they will both happen?
1/16
in a cross of Aa Bb cc X Aa Bb Cc, what's the probability of obtaining an individual with genotype AA Bb Cc?
1/16
If you are tossing a six-sided die, what is the probability of getting either a 3 or a 4 on your third toss AND a 6 on your fourth toss?
1/18
What's the probability of obtaining an individual with the genotype bb from a cross between two individuals with the genotype Bb?
1/4
Cells from the fruit fly Drosophila melanogaster contain four pairs of chromosomes. What is the number of possible sets of chromosome orientations during meiosis I?
16
When type B blood is given to a person with type A blood
B antigen from the donor reacts with anti-B antibody in the recipient.
In pea plants, flower color is controlled by a pair of alleles where purple (P) is dominant to white (p). Stem length is controlled by another pair of alleles where tall (T) is dominant to short (t). These two allele pairs segregate independently. Suppose you have a pea plant that has purple flowers and tall stems and you wish to carry out a testcross in order to determine its genotype. Complete the predictions using the correct terms.
In order to carry out the testcross, you should cross your original pea plant with another pea plant whose phenotype is white flowers and short stems. If you examine 100 F₁ plants from the testcross and find that they all have purple flowers with tall stems, you should conclude that the genotype of your original pea plant is PPTT. If you examine 100 F₁ plants from the testcross and find that 44 have purple flowers with tall stems and 56 have purple flowers with short stems, you should conclude that the genotype of your original pea plant is PPTt. If you examine 100 F₁ plants from the testcross and find that 53 have purple flowers with tall stems and 47 have white flowers with tall stems, you should conclude that the genotype of your original pea plant is PpTT. If you examine 100 F₁ plants from the testcross and find that 23 have purple flowers with tall stems, 26 have white flowers and tall stems, 24 have purple flowers with short stems, and 27 have white flowers with short stems, you should conclude that the genotype of your original pea plant is PpTt.
When genes lie near each other on the same chromosome, they do not follow Mendel's Law of Independent Assortment. What would you predict about the inheritance of two such genes?
Offspring will inherit the same two alleles that were passed down together from a grandparent.
In humans, the allele for dimples (D) is dominant to the allele for no dimples (d). At another gene locus, the allele for broad eyebrows (B) is dominant to the allele for slender eyebrows (b). These two allele pairs assort independently. A man who is heterozygous for both traits marries a woman who has no dimples and who is heterozygous at the gene locus controlling eyebrow width. Complete the sentences about this cross with the correct terms.
The genotype of the man is DdBb. The genotype of the woman is ddBb. The genotype of the gametes produced by the man is 25% DB, 25% Db, 25% dB, 25% db. The genotype of the gametes produced by the woman is 50% dB and 50% db. The probability that their first child will have dimples is 1/2. The probability that their first child will have dimples and slender eyebrows is 1/8.
In pea plants there is a dominant allele (A) for green pods and a recessive allele (a) for yellow pods. Suppose a heterozygous plant is crossed with a plant that has yellow pods. Complete the sentences about this cross with the correct terms.
The phenotype of the heterozygous plant is green pods. The genotype of the heterozygous plant is Aa. The genotype of the plant with yellow pods is aa. The genotype of the gametes produced by the heterozygous plant is 50% A and 50% a. The genotype of the gametes produced by the plant with yellow pods is 100% a. The expected frequency of F₁ plants with yellow pods is 50%. The expected frequency of F₁ plants with the genotype AA is 0%.
mendel's model assumes that each trait is determined by a single factor with alternate forms. we now know that this is too simplistic and that
a single gene can affect more than one trait, and traits may be affected by more than one gene
allele
alternative form of a gene
Epistasis
behavior of gene products can change the ratio expected by independent assortment even if the gene are on different chromosomes that do exhibit independent assortment
codominance
heterozygote shows some aspect of the phenotype of both homozygotes Type AB blood
Prior to the 20th century, the most common explanation of inheritance can best be described as
inheritance results from a blending of traits within fixed, unchanging species.
A trait is most likely to exhibit continuous variation if it is controlled by
many gene loci, each with several possible alleles.
multiple alleles
may be more than 2 alleles for a gene in a population Ex. ABO blood types in humans (3 allleles)
You are tossing a six-sided die. Because you cannot roll both a 2 and a 5 on a single toss, these two events are called
mutually exclusive
polygenic inheritance
occurs when multiple genes are involved in controlling the phenotype of a trait phenotype is an accumulation of contributions by multiple genes
pleiotropy
refers to an allele which has more than one effect on phenotype Pleiotropic effects are difficult to predict, because a gene affects one trait often performs other unkown functions one defective allele can cause multiple diseases
f2 generation
second filial generation offspring resulting from self fertilization of f1 plants recessive gene appeared among some f2 plants
The physical basis for the segregation of alleles when gametes are formed is
separation of homologous chromosomes during anaphase I followed by separation of sister chromatids during anaphase II.
The physical basis for the independent assortment of alleles when gametes are formed is
the independent alignment of homologous pairs during metaphase 1
