TOPIC: Meiosis, and Genetics
Cell Division General
Haploid – having one set of chromosomes (n) – gametes – sperm/egg
Diploid – having two sets of chromosomes (2n) – body cells – one set is maternal and one is
paternal
Plants cells do not have centrioles to do cell division
Steps to cell Division
Interphase
Cell spends most of its time = resting phase
Steps
1. G1- cell grows
2. S – DNA is synthesized
3. G2- all other organelles are copied
Meiosis Overview
Cell division
Produces four different haploid daughter cells (gametes)
Occurs in sex cells to form gametes
Steps of Meiosis
Meiosis involves 2 divisions – Meiosis I and Meiosis II
Meiosis I has some special events:
Prophase I homologous chromosomes pair up and crossing over occurs.
This recombination increases genetic variation for the species
Metaphase I – Pairs line up
Anaphase I – pairs are separated
Meiosis II is similar to mitosis
*** sexual reproduction – reproduction involving two parents
Advantage – genetic diversity, easier to evolve
Disadvantage – two parents, slower, more energy needed
REVIEW QUESTIONS
MITOSIS
MEIOSIS
Number of cells produced
2
4
Where does it take place
Somatic cells
gametes
Number of parents involved
one
two
How does it get variation
Mutation only
Sexual reproduction
TOPIC: Genetics
Inheritance
• Traits are specific characteristics inherited from parents
• Genes are the factors that determine traits
• The different forms of a gene are called alleles
• We have two genes for each trait – this is our GENOTYPE
• One gene came from mom, one from dad
• Introduction of a new member to a population increases genetic
Variation
 All organisms share the same genetic code.
 Order of nitrogenous bases determines phenotype
Genotype
actual alleles an individual has for a trait (letters)
Homozygous
• Both alleles are the same Ex. BB or bb
Heterozygous
• Both alleles are different Ex. Bb
Dominate or Recessive
• Dominant alleles are expressed, if present, and recessive are hidden
Phenotype
 The actual characteristic displayed by the individual (ex. brown eyes, Hemophiliac)
REVIEW QUESTIONS
8. In the Punnett square to the left, T = tall and t=short. Give the
parents genotypes.Heterozygous
9. Give the phenotype for the parents. Tall
10. What are the genotypes and phenotypes of the offspring?
Genotype : 25%TT, 50%Tt, 25tt
Phenotype: 75% tall, 25% short
11. What is the genotypic ratio of the offspring?
12. What is the phenotypic ratio of the offspring?
Codominance
• Heterozygote expresses BOTH dominant and recessive traits
• Ex. Roan animals, blood type AB, spotted chickens
Incomplete Dominance
• Heterozygote shows a blending of the dominant and recessive phenotypes
Polygenic traits
• Traits are influenced by more than one gene
• Ex. skin color, height, hair color
1:2:1
Multiple Alleles
• More than two alleles for a trait (an individual still only inherits two)
• Ex. Blood Type (IA,IB, i)
type A = IAIA or IAi
type O = ii
type B = IBIB or IBi
type AB= IAI
REVIEW QUESTIONS
13. Some genes produce intermediate phenotypes. Cross a pure breeding red flower (RR) with a pure
breeding white flower (WW). Give the genotypes and phenotypes of the offspring.
WR = PINK
14. What type of inheritance is this? ___incomplete dominance
15. If a woman with type A blood has a child with a man with type B blood and their first child has type O
blood, give the genotypes of the woman and the man and do the cross. (Alleles are IA, IB, and i)
Iai, Ibi
16. What are the odds that they will have a child with type O blood again? ______25%______
17. What are the odds that they will have a child with homozygous type A blood? ___0%__________
18. What are the odds that they will have a child with type AB blood? ______25%________________
19. A blood test is done to see if one of three men is the father of a child. The child has type O blood, the
mother has type A blood. Man #1 has type AB blood, Man #2 has type A blood, Man #3 has type O blood.
Are there any men that can be ruled out as the father? Explain .Man #1 he has no gene for type O blood
20. Using 3 genes (A,a and B,b and C,c) explain hair color in terms of these genes. How many phenotypes
are possible? 27
Sex-linked Traits
• Sex Chromosomes
– Female = XX
– Male = XY
• Sex linked traits are carried on the X chromosome
• Ex. Hemophilia, red-green colorblindness
• For a female to inherit the trait the father must have it and the mother must at least be a carrier
Test Cross
• used to determine the phenotype of an unknown dominant individual
• uses a homozygous recessive individual as the “test”
REVIEW QUESTIONS
21. What are the sex chromosomes in males? ____XY_________ In Females? _____XX_________
22. Colorblindness & hemophilia are sex-linked traits. What chromosome location (#) are these genes found?
X
23. Cross a female who is a carrier for hemophilia with a normal male. ___XBXb______ x ___XbY_______
24. What are the odds that they will have a child with hemophilia? ______25%________
25. What are the odds that they will have a daughter with hemophilia? 0%
26. What are the odds that they will have a daughter who is a carrier for hemophilia? __0%____
27. Why are males more likely to show this type of disorder? (Who (mother/father) is likely to give them the
bad gene?)
28. Double check your learning, solve the following genetics problem:
A brown mink crossed with a silverblue mink produced all brown offspring. When these F1 mink were
crossed among themselves they produced 47 brown animals and 15 silverblue animals (F2 generation).
Determine all the genotypes and phenotypes, and their relative ratios, in the F1 and F2 generations.
F1 100% Bb, 100% brown
F2 25% BB, 50% Bb and 25%bb
Pedigree
• similar to a family tree
• Shows pattern of inheritance of a specific trait through a family
REVIEW QUESTIONS
29. Using A,a, what is the genotype of person
II4?
aa
30. What is the genotype of person I3?
Aa
Karyotype
A chart showing arrangement of chromosomes
• In humans, 22 pair of autosomes
• 1 pair of sex chromosomes
• XX = female
• XY = male
• Extra chromosomes a result of nondisjunction
• Chromosome pairs fail to
separate in meiosis during prophase I
• One example is DOWN
SYNDROME (extra 21)
• Another example is
KLINEFELTERS (XXY)
REVIEW QUESTIONS
31. What is the gender of the person whose karyotype
is shown to the left? ____frmale______
32. What is the disorder that this person has?
Trisomy 21 (Down Syndrome)
33. What is your evidence?
Two x chromosomes and 3 #21 chromosomes
Human Genome Project
• Sequencing of human DNA
• Being used to develop gene therapies
Clone
• An organism made from one cell of another organism
• A genetically identical copy
Gel Electrophoresis
• Technique used to separate molecules (DNA or proteins) based on their size
• Sometimes called a DNA fingerprint
• Used to analyze and compare DNA
• IF DNA matches, it’s from the same individual
• Smaller strands travel farther
REVIEW QUESTIONS
To the left is an electrophoresis gel, showing evidence from a rape case.
34. Could the defendant be the rapist? (Y/N) __________
No, not a match
35. Which fragments of DNA are the longest? Explain.
At the top
36. What other ways can DNA fingerprinting be useful?
Finding lost relatives, proving paternity
Explain your answer.