Lesson 3: Pattern of Inheritence

homologous chromosome

matched pairs of chromosomes, one inherited from each parent, that have the same length, the same gene order, and the same centromere position, but may differ in their specific gene forms (alleles)

sister chromotids

two identical copies of a single, replicated chromosome, joined together at the centromere by a protein complex

ploidy (n)

number of complete sets of chromosomes in a cell

chromosome number

the actual value of n (or total number of chromosomes in one cell)

human somatic cell

diploid; 2n=46; 23 chromosomes but 2 copies of each

human gamete cell

haploid; n=23;

c-value

the mass (in picograms) of DNA contained within a haploid nucleus

2n, 2c

ploidy & c-value before DNA replication

2n, 4c

ploidy and c-value after DNA replication

n, 2c

ploidy and c-value after meiosis 1

n, c

ploidy and c-value after meiosis 2

2n, 2c

ploidy and c-value after mitosis

autosomal dominant

• rare

• males and females are equally affected

• affected individuals have an affected parent

• doesn’t skip generations

x-linked recessive

• rare

• males affected more frequently

• skips generations

• unaffected individuals have affected children

• never have father to son transmission

autosomal recessive

• rare

• males and females equally effected

• unaffected individuals have affected individuals

• skips generations

• becomes more common with inbreeding