Lecture 29- Mendelian genetics

More complex traits such as height are controlled by?

Genes

What is the correct hypothesis of inheritance ?

Particulate inheritance

Hybridization

Cross pollinated two contrasting true breeding varieties

2 fundamental principles of genetics

1. Law of segregation

2. Law of independent assortment

Alleles

The alternative version of “heritable units” that can e passed on to progeny

How did alleles arise?

Arise from mutations of the DNA sequence of a gene

4 Mendels conclusions

1. The alternative versions of heritable units can be passed on to progeny

2. For each character, an organism receives 2 copies of any given gene, one from each parent

3. If alleles differ at a locus, then one must be dominant

4. The law of segregation

Dominant allele

Expression is dominant

Phenotype is dominant

Masks expression of another allele

Recessive allele

Expression is masked by another allele

Phenotype is recessive (if 2 copies of the recessive allele)

Law of segregation

The 2 alleles for a heritable character segregate (separate from each other) during gamete formation and end up in different gametes

Homozygote

If an organism has a pair of identical alleles for a gene

Heterozygote

If an organism has a pair of alleles for a gene that are different, it is a heterozygote

Monohybrid cross

Follows only one character

Law of independent assortment

States that 2 or more genes will assort independently into gametes

What causes linked genes?

If genes are really close on a chromosome, they are “linked”. Alleles of these genes will be packaged into chromosomes together during meiosis.

If genes are really far apart on the same chromosome, what are the odds of crossing over between them?

Very likely ( approaching 100%)

What stage in meiosis would the law of segregation occur ?

Anaphase I

What is true about a plant with the genotype AABbcc?

Homozygous at 2 loci

Where does independent assortment occur?

Meiosis I