AP BIOLOGY 11. Genetics: Chapter 14 & 15 Pg. 247 - 286. Mendel’s Laws. Gregor Mendel is credited with discovering the basic principles of genetics These principles or Laws have seen many modifications but basic genetics begins here. Mendelian genetics. Character
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Genetics: Chapter 14 & 15
Pg. 247 - 286
(heritable feature, i.e., fur color)
(variant for a character, i.e., brown)
(crossing of 2 different true-breds)
(first filial generation - hybrid)
(result of self-pollination from F1)
Dominance and Recessive
Example: yellow peas dominant over green; round pea is dominant over wrinkled
Note: The dominant recessive interaction can be
interpreted differently depending on your level of
study as - a whole organism, a bio-chemical level
or a molecular level E.g. Tay-Sachs disease pg. 256
Law of Independence Assortment
During meiosis, the different homologous chromosome assort independently from other homologous chromosomes
Law of Segregation
The alleles for each character segregate (separate) during meiosis I. (homologous pairs separate)
Only one of the allelic pair are in each sex cell
Cross between parents that differ at a single allelic pair (usually AA x aa)
Cross between parents that differ at two allelic pairs (AaGg X AaGg)
Law of Independent Assortment
Are All Random Events……
1. Rule of Multiplication
Problem: If two parents are YyRr, what is probability of them conceiving a yyrr offspring?
2. Rule of Addition
The probability of the dominant from mother and recessive from father is: 1/2 x 1/2 = ¼
The probability of the dominant from father and recessive from mother is: 1/2 x 1/2 = 1/4
Therefore, the overall probability is the sum of these two probabilities: 1/4 + 1/4 = ½
Answer: The probability of them producing a heterozygous offspring is a 1 in 2 chance or a 50% chance
1. What is the probability of rolling two 6’s from two dice at the same time?
2. What is the probability of getting a heads - tails combination when tossing two coins simultaneously?
3. Two parents are AaBbCc - what is their probability for a aabbcc offspring?
1. Pigeons can be either plain or checkered color. A series of crosses were made, and the following ratios were observed:
Cross 1: Plain x Plain = All Plain;
Cross 2: Checkered x Checkered = All Checkered;
Cross 3: Checkered x Plain = 1 Checkered:1 Plain;
Cross 4: Checkered x Checkered = 3 Checkered:1 Plain.
Which phenotype is dominant? Create your own gene symbol and give the genotypes of the parents (as close as you can determine) for each cross.
2. In humans, the allele which confers the ability to roll the tongue is dominant over the allele which does not confer the ability to roll the tongue. If a man who can roll his tongue and whose mother could not mates with a woman who cannot roll her tongue, what proportion of the children would be expected to be able to roll their tongues if they have a large number of children? What are the genotypes which are possible among the children?
3. In humans, the gene for dimples is recessive to its allele which produces no dimples. Also, the gene for 5 digits per hand and foot is recessive to its allele for 6 digits per hand and foot. Cross a man who does not have dimples, who has 6 digits per hand and foot, heterozygous for both these traits with a women who has dimples and 5 digits per hand and foot. What phenotypes might be present in their children? What is the probability at conception for each phenotype occurring?
4. A student did a series of genetic crosses on pea plants examining tallness and seed color. What type of cross would produce the following offspring genetic ratios?
Both alleles are expressed resulting in a blending of traits
Example: snapdragons can be red or white, but in the heterozygous condition, they are pink
This occurs when both members of an allelic pair are expressed - not blended.
Example: blood types - Type A and Type B are co-dominant. The heterozygous condition is Type AB
Note: Dominance ranges from complete dominance, through to various degrees of incomplete dominance, to codominance
Ex: Chicken combs are controlled by two genes producing four possible phenotypes (dihybrid cross
Epistasis: a gene at one locus (chromosomal location) affects the phenotypic expression of a gene at a second locus. The interaction between two or more genes to control a single phenotype Ex: mice coat color
9 B_D_ (black)
3 B_dd (dilute black)
3 bbD_ (brown)
1 bbdd (dilute brown)
Sex Linkage (pg. 277-279)
The white eyed fruit fly is a male that inherited a single sex linked mutant gene for eye color. The red eye male is normal.
a. A male with red eyes crossed with a female with white eyes
b. A heterozygous female crossed with a male with red eyes
c. A heterozygous female crossed with a male with white eyes
d. A homozygous red-eyed female crossed with a male with
2. A couple have a son with sex-linked muscular dystrophy.
a. From which parent did the son receive gene(s) for muscular dystrophy?
b. If their next child is a girl, what is the probability she will inherit sex-linked muscular dystrophy?
c. If their next child is a boy, what is the probability he will inherit sex-linked muscular dystrophy?
d. What is the probability of them having three sons in a row all with muscular dystrophy?
e. This couple is expecting yet another child (after the three in d), what is the probability of this child having muscular dystrophy?
The pair of homologous chromosomes do not separate properly during meiosis I or sister chromatids fail to separate during meiosis II
What can you decipher
From the pedigree?
When boy III-1 (outlined in blue) died suddenly at a football game at the age of 19, his mother II-2, brother and sisters, friends and doctors were confused. An autopsy showed that the young athelete had died from familial hypertrophic cardiomyopathy (HCM), an inherited disease of the heart muscle. condition.