Describe what occurs during "crossing over", including when it occurs.
Occurs during prophase 1 of Meiosis
Is the process where homologous chromosomes pair up with each other and exchange different segments of their genetic material to form recombinant chromosomes
If an organism's diploid number is 36, its haploid number is _____.
What are the two main sources of genetic variation?
1. Random (independent) assortment of genes during meiosis
2. Crossing over during meiosis 1
What's taking place in the diagram?
A woman that is heterozygous for widow's peak and heterozygous for freckles mates with a man that is also heterozygous for both traits. What is the phenotypic ratio of their possible offspring?
9 with freckles AND widow's peak
3 with freckles and no widow's peak
3 with widow's peak and no freckles
1 with neither widow's peak nor freckles
The passing of characteristics from parents to offspring
The study of the passing of characteristics from parents to offspring
Who was the father of modern genetics?
Differentiate between true breeding and hybrid breeding.
True breeding creates offspring identical to each other and the parents
Hybrid breeding creates offspring that are different.
What did Mendel determine?
That biological factors (genes) are passed from parents to offspring.
The principle of dominance states that
Some alleles are dominant and some are recessive
Hair color and eye color are examples of ______, while blonde, brunette, blue, and green are examples of ______.
Alleles - different versions of a gene
How many alleles for each gene does a gamete possess?
Compare and contrast the terms homozygous and heterzygous.
Homozygous describes genotypes where both alleles are the same (ex. TT or tt)
Heterzygous describes genotypes where the alleles are different (ex. Tt, Hh, AB)
How do genotype and phenotype relate?
Genotype is the actual genes (ex. TT, Tt, tt)
Phenotype is the physical expression of the genes (ex. tall or short)
What are punnett squares used for?
Used to determine the gene combinations that might be possible from a genetic cross
What can't be determined from a punnett square?
The actual results of a genetic cross.
The Law of Independent Assortment states that
alleles of different genes separate independently of each other during gamete formation
True or false: genes on different chromosomes are related.
False: genes on different chromosome are not related in any way.
What is meant by the term "polygenic" and why is it significant?
The trait is controlled by many genes, as opposed to a single gene, and the expression of the trait contains a lot of variety (ex. hair color, skin color, eye color, height)
What is incomplete dominance?
A form of inheritance in which the dominant trait does not completely mask the appearance of the recessive trait. Blending of the dominant and recessive traits occurs with heterozygous individuals.
What is codominance?
With codominant traits, both alleles contribute to the expression of the gene so both forms of the gene are shown in the phenotype.
Ex. roan cattle, erminette chickens.
What form(s) of inheritance is exhibited by human blood types?
both codominance and multiple alleles
A form of inheritance in which there are multiple alleles for a single gene trait
Traits that are produced by the interaction of several genes
What does each symbol on a pedigree represent?
Square - male
Circle - female
Horizontal line - married couple
Vertical line - offspring
Filled in square/circle - possesses the trait
Half filled in square/circle - carrier of the trait
Slash - deceased
This form of inheritance does NOT skip generations (for a child to have it, at least one of their parents must have it), and is found in males and females in equal numbers
This form of inheritance DOES skip generations (a child can have it without the parent having it) and is found in males and females in equal numbers
Describe the characteristics of sex-linked (x-linked) traits.
- Mostly found in males
- If father has it then daughter has it OR is carrier
- If the son has it then the mother is a carrier
- Is carried on the x chromosome
Describe the products of meiosis.
4 genetically unique haploid cells (N), each with 23 chromosomes.
How many chromosomes do sex cells (gametes) contain?
The two types of gametes are
Sperm and egg cells!
How does meiosis differ in males and females?
In males - produces 4 sperm cells
In females - produces 1 egg and 3 polar bodies
Reductive cell division
Compare and contrast haploid and diploid
Haploid - cells that contain half the normal chromosome count, represented by the symbol "N", are gametes
Diploid - cells that contain the full chromosome count, represented by the symbol "2N", are somatic cells
When are the homologous pairs separted?
During Anaphase I
When are the sister chromatids separated (during meiosis)?
During Anaphase II
How might a human cell end up with an incorrect chromosome number at the end of meiosis?
What is nondisjunction and what is the term for cells that suffer from this phenomenon?
Nondisjunction is a failure of chromosomes to separate correctly.
Cells that suffer from this possess aneuploidy, an abnormal chromosome number.
What is a karyotype and what is it used for?
A karyotype is a picture of a person's chromosomes.
It can be used to detect an extra or missing chromosome, and indicate if an individual is male or female.
What chromosomes would you expect to find in a human egg cell?
22 autosomes and an X chromosome
Which chromosomes would you expect to find in a human sperm cell?
22 autosomes and a Y chromosome