Biology Exam Review Grade 11 - GENETICS

Unit 2 - Genetics part 1 and 2

How many chromosomes and SETS of chromosomes do humans have?

We have 46 chromosomes and 23 sets

What is the structure of a chromosome?

The DNA is tightly wound around a histone, and forms a nucleosome. Multiple of these form chromatin, which makes up a chromatid. There are also telomeres at the ends of each chromatid. 2 chromatids are held together with a centromere

how many chromosomes are inherited from each parent

You get 23 chromosomes from your mother and 23 from your father, totaling 46 chromosomes (23 pairs) in each cell

Define alleles

Alleles are variants of genes

Define dominant

A dominant trait is a trait that can easily overrule the other trait.

Define recessive

A recessive trait is a trait that can be easily overrruled by the other trait.

Define genotype

the complete set of an organism's genetic instructions, essentially its entire DNA blueprint containing all the information needed to build, function, and maintain that living being

Define hybrid

An offspring resulting from the combination of two genetically different parents, such as different species, subspecies, breeds, or varieties, inheriting traits from both.

Examples: Liger

How do cells turn DNA into proteins?

Step 1: The DNA is transcribed into mRNA. The DNA hydrogenous bases are unzipped by a special enzyme that builds a complementary RNA strand on it. This strand is known as mRNA
Step 2: This mRNA makes its way to the ribosomes for protein synthesis.
Step 3: The tRNA brings amino acids to the ribosome and attaches the corresponding amino acid to the right codons. As this is happening, the amino acids are bonded with peptides
Step 4: After the ribosome hits a stop codon, the mRNA is turned into a polypeptide chain. The polypeptides are folded into proteins
Step 5: The proteins go to the rough E.R for quality control and folding, and then they are sent to the Golgi Apparatus to be modified, stored, and packaged.

Describe the stages of mitosis

Interphase - growth 1 - regular lifecycle, synthesis - chromosomes duplicate and prepare for division, growth 2 - growth prep for mitosis

Prophase - Centrioles go to opposite ends of the cell, nuclear membrane starts to disappear, spindle fibres start to form, nucleolus disappears, chromosomes condense

Metaphase - chromosomes line up on metaphase plate and spindle fibers attach

Anaphase - Chromosomes are pulled apart to opposite ends of the cell

Telophase - Nuclear membrane begins to reform, spindle fibers break down

Cytokinesis - Cell splits

2 diploid daughter cells are formed

Describe the stages of meiosis

Interphase 1 - Original cell is diploid. DNA and chromosomes are doubled. Growth and synthesis occur

Prophase 1 - chromosome pairs join together at the centromere to for tetrads. The alleles cross over and the nuclear membrane disappears. Spindle fibres also start to form

Metaphase 1 - Tetrads line up at the metaphase plate

Anaphase 1 - tetrads are pulled apart to form homologous chromosomes

Telophase 1 - Chromosomes uncondense and nuclear membrane begins to reform. Cells divide and 2 different haploid (23 chromosome) cells are formed

Interphase 2 - Brief period of growth and protein replenishment

Prophase 2 - Same as prophase 1 but no crossing over and different chromatids.

Metaphase/anaphase 2 - same except each chromosome gets pulled apart to chromatids

Telophase 2 - End up with 4 individual haploid cells with genetic diversity

Describe what a silent mutaton is

A silent mutation occurs when there is a change or problem in a chromosome, but that change does not result in a change in phenotype.  (the mutation is not expressed, the individual functions normally)

1. Mutations that occur in non-coding DNA (junk DNA) 

   1. The DNA is altered but no structures or chemicals are made from it

2. Recessive mutations in diploid organisms

   1. This mutation can be silent for me but not for my kids if me and my partner both have recessive genes to form a homozygous recessive allele. 

Explain the types of genetic mutations

Point mutations - Only one point in the gene is incorrect, so only one gene malfunctions. Usually minor, but can be dangerous. Example: Colour blindness: When cone cells in the retina don’t work properly

Chromosomal Deletion - A piece of a chromosome is broken off or goes missing, so genetic information is lost and cannot be passed down. Because of this, body parts can’ be properly made. Caused by unequal crossing over/synapsis. Example: Angleman’s syndrome

Polyploidy - This happens when cells do not go through the second division of meiosis, and a gamete with too many chromosomes is produced. 3n cell, Gametes have a full set of chromosomes + 1 ½. Examples: In lizards: they can grow back tails. In humans: can cause miscarriage and even death of the child after birth.

Describe what happens during nondisjunction

Chromosomes fail to separate properly during meiosis, resulting in gametes with abnormal numbers of chromosomes. Examples: Down syndrome - Extra chromosome 21 (trisomy 21)

Difference between Trisomy and monosomy

Trisomy is when each cell has 22 pairs of chromosomes and one set of chromosomes with 3 pairs, and monosomy is when each cell has 22 pairs of chromosomes and one set of chromosomes with only one. Trisomy is when there is an extra copy of a chromosome (47), and monosomy is when there is an absence of one copy of a chromosome (45).

Describe incomplete dominance

Occurs when a heterozygous individual expresses a 3rd phenotype that’s a blend between the other 2 phenotypes. Neither is dominant.

Example: let b be black, let w be white, let bw be grey

Describe co-dominance

Occurs when a heterozygous individual expresses a 3rd phenotype where both phenotypes are expressed at once. Neither is affected by eachother.

Example: let b be black, let w be white, let bw be black and white stripes

Describe Mendel’s 3 laws of segregation

1. Offspring receive one factor (allele) from each parent for each inherited trait.

2. For each trait there is a dominant factor (allele) and a recessive factor (allele).

3. There is an equal chance that a parent will donate either factor to their offspring