Download Notes: Chromosomes and Meiosis Gametes have half the number of

Notes: Chromosomes and Meiosis
Gametes have half the number of chromosomes that
body cells have.
chromosome
chromosome
Gene A
Gene B
Gene C
Replication
centromere
Gene D
GENE: a section of
DNA that directs a cell
to make a certain
protein
Sister
chromatid
You have somatic cells and gametes.
Somatic (body) cells:
• Make up body tissues & organs
• DNA in these cells are NOT passed on to offspring
body cells
You have somatic cells and gametes.
Gametes:
• Are sex cells like sperm and egg
• DNA in these cells ARE passed on to offspring
sex cells (sperm)
sex cells (egg)
Each cell has autosomes and sex chromosomes.
• Your body cells have 23 pairs of
chromosomes.
1. (22) AUTOSOMES contain
genes that determine body
information (hair color, eye
color, hair texture, etc.)
2. (1) pair of SEX
CHROMOSOMES determine
sex (XX=female; XY=male).
3. HOMOLOGOUS PAIRS of
chromosomes have the same
structure (size, genes)
Body cells are diploid; gametes are haploid.
• Fertilization between egg and sperm occurs in sexual
reproduction.
• Diploid (2n) cells have two copies of every chromosome.
– Each comes from each parent
• Haploid (n) cells have one copy of every chromosome.
– Gametes are haploid.
– Gametes have 22 autosomes and 1 sex chromosome.
Mitosis
• Produces genetically
identical cells
• Results in diploid cells
• Occurs throughout
organism’s lifetime
• Asexual reproduction
Meiosis
• Produces genetically
unique cells
• Results in haploid cells
• Occurs during certain
times of one’s life cycle
• Sexual reproduction
• ALLELE: any alternative form of a gene occurring at a specific
locus on a chromosome.
– Each parent donates
one allele for every
gene.
– Homozygous
describes two alleles
that are the same at a
specific locus.
– Heterozygous
describes two alleles
that are different at a
specific locus.
Genes influence the development of traits.
• A genome is all of an organism’s genetic material
• A GENOTYPE refers to the combination of a specific set of
genes.
– Homozygous
describes two alleles
that are the same at a
specific locus/location.
– Heterozygous
describes two alleles
that are different at a
specific locus/location.
Genes influence the development of traits.
• A PHENOTYPE is the physical expression of a trait; what
you actually see.
• Alleles can be represented using letters.
– Dominant alleles are
expressed as the phenotype;
the stronger allele;
represented by capital letters
– Recessive alleles are
considered the “weaker allele”
and is expressed only when
two copies are present;
lowercase letters