Biology 10 Lecture
Chapter 23 - Patterns of Gene Inheritance
I. Overview
A. Mendel’s Laws
B. Genetic Disorders
C. Beyond Simple Inheritance Patterns
II. Mendel’s Laws
A. DNA in chromosomes contain thousands of segments called _____
1. Genes in DNA direct the formation of __________ in cells, thus determine inherited
________
2. Genes have specific ______ sequences and are found in particular regions, called
______ (sgl., locus), on a chromosome
3. _________ are genes that control the same trait (e.g., eye color), and are found in the
same loci on _____________ chromosomes.
4. Alleles are represented by paired __________ (e.g., BB, Bb, bb)
a. ______________ allele: gene that controls for a trait that is _________ whether it’s
paired with another dominant allele or with a recessive allele.
1) _____________ dominant has 2 of the same dominant alleles (e.g.: BB).
2) _____________ has one dominant and one recessive allele (e.g.: Bb). An
individual that is heterozygous for a trait is often called a ________ of the
trait.
b. _____________ allele: gene that controls a trait that is only evident if the allele is
paired with another recessive allele.
1) Homozygous recessive has 2 of the same ___________ alleles (e.g.: bb).
B. Gregor __________ (Austrian monk 1860): Father of ________
1. Experimented on pea plants and discovered that each pea plant trait is controlled by 2
“__________” (alleles).
2. One factor was __________ (e.g., yellow seeds) over the other, which was
____________ (e.g., green seeds).
3. His findings led him to formulate the _____ of segregation and independent
assortment
C. Segregation and Independent Assortment of Chromosomes (and their alleles) occurs
during _________.
1. Law of ____________ ____________
a. Each pair of homologous chromosomes can align (assort) itself in ____ possible
ways in ____________ I and does so independently of the other chromosomes.
b. All possible ____________ of homologues can occur in the gametes (sperm and
egg).
c. This law is used when solving genetics problems involving alleles on __________
pairs of homologous chromosomes
2. Law of ______________
a. Each homologous pair of chromosomes has two ________ for each trait.
b. The chromosomes and their alleles __________ (separate) during ____________
I.
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c. Each resulting gamete contains only ___ chromosome and its _________ from
each homologous pair.
d. Fertilization gives the new individual ___ alleles for each trait.
e. This law is used when solving _____trait genetics problems.
D. Inheritance of a ______ Trait with alleles on same pair of homologous chromosomes
(___________ Dominance). Terms:
1. ___________ - type of genes an individual has for a particular trait(s) (e.g.: ___ =
homozygous dominant, ___ = heterozygous, ___ = homozygous recessive).
2. ___________ - physical or observable characteristics that result from the genotype
(e.g.: widow’s peak vs continuous hairline).
3. Gamete Formation – because segregation of alleles occurs during meiosis, each
gamete will contain only ___ of each type of allele.
4. Punnett Square - device used to determine the ____________ of possible genotypes
and phenotypes of simple genetic crosses. Directions for creating punnett squares
(Widow’s peak activity):
a. Determine ___________ of P (parental) generation and all possible __________
in their gametes. W=widow’s peak, w=straight hairline.
b. For this exercise, assume both parents are _____________ (heterozygous=Ww),
so each of their gametes would contain a dominant (W) or a recessive (w)
allele].
c. Align all possible combinations of _____ vertically and ___ horizontally (or vice
versa).
d. Merge egg & sperm alleles in converging squares, then determine probable
proportions of ___________ and ________ of children (F = filial generation).
e. Monohybrid cross always results in ___:__ phenotypic ratio of offspring.
f. Chance has no memory - each new child has the same ___________ of
genotypes & phenotypes.
5. One Trait __________
a. Used to determine whether an individual with a _________ phenotype is
homozygous dominant or heterozygous by crossing with a homozygous
____________ individual.
b. No recessive phenotype offspring indicates that the parent is homozygous
___________.
c. Any offspring with recessive phenotype indicates that the parent is
_____________
E. Inheritance of _____ Traits on Different Pairs of Homologous Chromosomes (Complete
Dominance). Directions:
1. Determine parental ___________ (we’ll assume both parents are ____________ WwSs x WwSs). W=widow’s peak, w=straight hairline; S=short fingers, s=long
fingers.
2. Determine all possible ________ combinations in gametes, remember that each
gamete receives only ___ of each allele (e.g.: ___, ___, ___, ___).
3. Set up a Punnett Square with ___ squares.
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4.
5.
Join _________ from gametes in converging squares.
Determine _____________ ratio of offspring from resulting genotypes. (Dihybrid
cross always results in 9:3:3:1 phenotypic ratio.)
III. Genetic Disorders (__________) - Many human disorders are due to abnormalities of single
allele pairs.
A. ___________ charts can determine if a disorder is inherited.
1. Males are represented by _________, females by _________.
2. Horizontal line between circle & square represents a _______.
3. Vertical lines extend down to _____________ from union.
B. Autosomal ____________ Genetic Disorders
1. Caused by a __________ allele on an autosomal (not sex) chromosome.
2. A child and at least one _________ is affected.
3. Example: ________________’s Disease
a. Result of an abnormal gene on chromosome __.
b. Disease does not usually develop until ___________ age.
c. Causes degeneration of _______ cells; person gradually loses control of muscle
function and dies.
4. Do Punnett square of autosomal dominant disorder.
C. Autosomal __________ Genetic Disorders
1.
Disorder is only present if both alleles for the trait are _______ on homologous
chromosomes.
2. Parents are usually heterozygous ________ of a recessive gene.
3. Homozygous recessive _______ is affected but parents are not
4. Example: Phenylketonuria (____)
a. Result of abnormal gene on chromosome ___.
b. Caused by lack of enzyme to break down ______________ (an amino acid).
c. ________________ accumulate in blood & urine.
d. Newborns are routinely tested for ____ in hospitals.
e. Diet low in ______________ can prevent mental retardation.
5. Do Punnett square PKU practice problem.
IV. Beyond Simple Inheritance Patterns
A. _____________ Inheritance
1. Controlled by two or more sets of ____________, often on different pairs of
homologous chromosomes.
2. Different alleles may have an __________ effect on the trait.
3. Example: skin ________.
a. Couple with dark and light skin have ___________ skin color children.
b. Couple with medium brown skin color have children with skin colors from
_______ to _________.
4. Polygenic Disorders include ______, diabetes, hypertension, and many others.
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B. ___________ Alleles
1. Within a population, there may be __ or more alleles that affect the same trait.
2. Each person still has only ___ of the alleles for the trait.
3. Example: _____ Blood Types
a. Type __ has __ antigen on RBC surface and antibodies against __ antigen; alleles
are AA or AO (A is dominant).
b. Type __ has __ antigen on RBC surface and antibodies against __ antigen; alleles
are BB or BO (B is dominant).
c. Type ___ has __ & __ antigens on RBC surface and no antibodies against __ or
__; alleles are AB (codominant).
d. Type __ has no _______ on RBC surface, but has ________ against A & B
antigen; alleles are OO (recessive alleles).
e. Do Punnett square on how to determine blood type.
4. ___ Factor
a. Inherited separately from ____ blood types.
b. Rh+ has _________ on RBC surface, Rh- does not.
c. If Rh- woman marries Rh+ man, fetus may be ___.
d. Rh- mother exposed to Rh+ fetus’ blood builds up _________ against Rh+ blood.
e. If subsequent baby is Rh+, mother’s ____________ can cross placenta and destroy
the fetus’ RBCs.
C. Incomplete & Codominance
1. Occurs when neither member of an allelic pair is _________ over the other.
2. _____________ - both alleles are expressed equally (e.g.: __ blood type).
3. ______________ Dominance – heterozygous genotype has an _____________
phenotype between the dominant and recessive. Example: _________ Cell
Anemia
a. A defective gene produces abnormal __________ (Hb), the oxygen-carrying
protein in RBCs, so they assume a _________ shape and clog arteries.
b. Genotype HbSHbS has full blown ________ cell disease.
c. Genotype HbAHbA has _________ hemoglobin.
d. Genotype HbSHbA (heterozygous) has the sickle cell _____ (a mild form of
the disease).
e. Sickle cell anemia more prevalent among persons from Africa, where
___________ is prevalent.
f. Sickle cell trait protects RBCs from effects of malaria, thus large numbers of
________________ are preserved in the population.