3.3 Review PBS

How is DNA passed to new cells during cell division?

• Mitosis– Makes two duplicate body cells– Used for growth and repair of cuts– Before the cell divides the DNA in the chromosomes will

replicate so each cell has the same DNA and same amount of chromosomes

How is DNA passed to new cells during cell division?

• Meiosis– Makes 4 different sex cells (gametes)– Used to divide chromosome number in half so sex cells can

combine during fertilization and produce a zygote with the same amount of chromosomes as the parent.

– Similar process as mitosis, but cells divide twice after DNA replicates to produce 4 cells with half as many chromosomes.

What is a chromosome? • Structures in the nucleus that are composed of the DNA

wrapped around a protein• Humans have 46 chromosomes in their body cells (only 23 in

sex cells)– There are 22 pairs of homologous chromosomes (chromosomes that

contain the same alleles in the same location)– Alleles – are one type of a gene. There are dominant and recessive

alleles.

What is a chromosome? • 46 chromosomes

– 44 or them or 22 pairs are autosomal chromosomes, which do not affect your gender

– 2 or 1 pair are sex chromosomes, which determine gender• XX is a female• XY is a male

• Karyotype– Picture of all the chromosomes in a cell

male female

How are traits passed through the generations?

• Parents pass on their genes to their offspring. • The genotype (genes) that child receives

determines their phenotype (appearance)– If a dominant allele is present then the person will

have the dominant phenotype– If only recessive alleles are present then the

person will have the recessive phenotype– Some individuals can be carriers (Bb) and pass on

the recessive allele even though they have the dominant phenotype