Meiosis, Genetics and Heredity
Meiosis – A Source of Distinction
At one level, the answers lie in meiosis.
This makes for a lot of genetic variation. This trick is accomplished through
______________________and ________________________
Crossing over – chromosomal segments are exchanged between a pair of
________________ chromosomes.
Independent Assortment-random distribution of alleles occurs
during ___________ formation.
Genetic Variation occurs in Asexual or
Sexual Reproduction?
Meiosis is Reduction Division
Chromosome number is cut in half by separation of homologous chromosomes in _______ cells
Differences Between Mitosis & Meiosis
• MITOSIS-Body Cells produces __ identical
_____(2n) cells
• MEIOSIS-Sex Cells produces __ different
_____(n) cells
• Body Cells (Mitosis)
Diploid (2n) – results in 2 genetically identical
diploid cells.
___________ (Meiosis)
Haploid (n) – results in 4 genetically _________
haploid cells.
Diploid: containing two
complete sets
1 of
chromosomes, one from
each parent.
Haploid: is the term used
when a cell has half the usual
number of chromosomes.
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Human Cells 2n=46.
Sperm Cell
– 23 chromosomes
– ________ is haploid (n)
Egg Cell
– 23 chromosomes
– Gamete is ________ (n)
White Blood Cell
– 46 chromosomes
– Body cell is _______ (2n)
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Nondisjunction
– The failure of homologous chromosomes to separate properly during meiosis
Introduction to Genetics
Genetics = the study of __________
•
Gregor Mendel
– Principle of _____________
– Law of ____________________
– Law of Independent ________________
– The Father of Genetics
– carried out important studies of heredity
• _______________—the passing on of traits from parents to offspring
• He studied _______________________
Chromosomes: Tightly coiled DNA where your _____ are carried
Genes: ________________________ that control your traits
•
Homologous Chromosomes: Chromosomes that are the
same size and shape and carry the____________. You get
___ from your mother and ___ from your father that
match up.
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Alleles (Genotypes)
– The different forms a gene can take. (Letters)
• 2 Types of Alleles:
– 1. Dominant - Represented by a
__________________  (Exp. A)
– 2. Recessive - Represented by a
__________________ (Exp. a)
– Trait- a ________________________ that is controlled by genes (Genotypes)
– Exp. Eye color, hair color, height
– Genotype
• The combination of two alleles (letters) that represent the _______________of
an individual. (AA, Aa, aa) (Alleles)
– Phenotype
• The observable ____________________of an individual that are the result of its
genotype. (Long eyelashes, Blue or Brown eyes) (Trait)
3 Types of Genotypes:
• 1. Homozygous Dominant
– 2 identical alleles that are _____________ (AA, TT)
• 2. Heterozygous
– 2 __________ alleles (Aa, Tt)
• 3. Homozygous Recessive
– 2 identical alleles that are _____________ (aa, tt)
Principle of Dominance
• An organism with a __________ allele for a particular trait will exhibit that form only
when the dominant allele for the trait is ___ present.
• Organisms with a heterozygous genotype (Aa) will never exhibit the recessive trait
because it is ___________ (masked) by a dominant allele.
Mendelian Exceptions
- Not all genes show simple patterns of dominant and recessive alleles
Because the majority of traits are controlled by more than one gene/alleles
There are some exceptions to Mendel’s Laws.
1. INCOMPLETE DOMINANCE
• Neither allele is completely dominant
• Both alleles _________________ to give a new trait.
• Called hybrids
• EX: red flower (RR) crossed with white flower (R’R’)
produces pink flower (RR’)
In snapdragons, flower color is controlled by incomplete
dominance. The two alleles are red (R) and white (W). The
heterozygous genotype is expressed as pink.
a) What is the phenotype of a plant with the genotype RR? ___________
b) What is the phenotype of a plant with the genotype WW?___________
c) What is the phenotype of a plant with the genotype RW? ___________
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2. CODOMINANCE
• ________alleles are expressed
• EX: cross a black chicken with a white chicken, offspring will be black
and white checkered. (erminette)
In some chickens, the gene for feather color is controlled by
codominance. The allele for black is B and the allele for white is W. The
heterozygous phenotype is known as erminette (black and white
spotted).
a) What is the genotype for black chickens? ____
b) What is the genotype for white chickens? ____
c) What is the genotype for erminette chickens? ____
Two erminette chickens were crossed. Show the Punnett square.
a) What’s the probability they would have a black chick? ____%
b) What’s the probability they would have a white chick? ____%
3. MULTIPLE ALLELES:
more than two alleles control a phenotype
• Ex: blood type
• Blood type = presence or absence of proteins on red blood cells
• Usually have to do more than one punnett square to determine possibilities for kids.
Human blood types are determined by genes that follow the CODOMINANCE (multiple
alleles) pattern of inheritance. There are two dominant alleles
(A and B) and one recessive allele (O).
*Write the genotype for each person based on the description:
a.
b.
c.
d.
e.
Homozygous for the “B” allele
Heterozygous for the “A” allele
Type O
Type “A” and had a type “O” parent
Type “AB”
______
______
______
______
______
Pretend that Brad Pitt is homozygous for the type B allele, and Angelina Jolie is type
“O.” What are all the possible blood types of their baby?
4. Sex-linked inheritance
•
Traits controlled by genes located on ___________________are called sex-linked traits.
•
•
The alleles for sex-linked traits are written as superscripts of the X or Y chromosomes.
When genes are located on the X chromosome, females receive _____ alleles for these genes, but
males only receive _____.
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•
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In males, the genotype is automatically known.
The small chromosome (y) does not
Males can pass it to all of their
carry an allele so whatever allele is
daughters, none to sons
• Colorblind male - XcY (recessive)
on the X (donated by mom) is what
• Normal male - XCY (dominate).
Females have 50/50 chance of
the boy will have.
A female can be:
passing it to all of their
• XCXC - normal
He is either completely dominant or
children
completely recessive
• XCXc - carrier
• XcXc – colorblind
Boys cannot be a carriers of a sex
•
linked trait.
H= normal blood clotting
h=hemophilia
A woman that is heterozygous for normal blood clotting is cross with a man that has normal
blood clotting. What are the chances that their offspring will have hemophilia?
5. Polygenic inheritance______________ genes affect the phenotype.
• Ex: height, weight, skin color, eye color
PEDIGREE CHARTS
A _________________________ of a genetic condition
• Pedigree charts show a record of the family of an individual
• They can be used to study the _____________________________________________
• They are particularly useful when there are large families and a good family record over
several generations.
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