SBI3U Grade 11 Biology Genetics Test 2

Thanks, Victoria!

Genetics Study Notes

 

Genetics: the field of biology that involves the study of heredity and variation of living organisms and how genetic information is passed from one generation to the next

 

Genetics: study of heredity, the process in which a parent passes certain genes onto their children; children inherit their biological parents’ genes that express specific traits.

 

DNA: molecule inside the nucleus that gives instructions to make proteins etc.

DNA Nucleotide includes:

  • 1 Phosphate group
  • 1 Deoxyribose Sugar
  • 1 Nitrogenous Base (Adenine, Thymine, Guanine, Cytosine)

Base Pair: AT and CG

  • Gene: segment of DNA that encodes information

 

 

Meiosis: process at which sex cells (gametes) with a haploid number of chromosomes are produced

 

Two Key Outcomes:

  1. Genetic Reduction: daughter cells produced have half the amount of genetic information (23 chromosomes)
  2. Genetic Recombination: products have different combinations of alleles (forms of a gene), genetically different offspring

 

Meiosis:

  • takes place in ovaries and testes
  • two nuclear divisions
  • human cell with 46 chromosomes (2n) will undergo meiosis, produce gametes with 23 chromosomes (n), known as gametogenesis
  • each gamete has 23 chromosomes
  • produces 4 haploid daughter cells that are genetically different
  • fertilization: haploid (n) sperm cell + haploid (n) egg cell = diploid (2n) zygote
  • zygote will produce multi-cellular organism

 

 

 

 

 

Vocabulary:

Chromosomes- humans have 46, 23 pairs, 1 pair of sex chromosomes, 22 pairs of autosomes, 2 sister cromatids held by a centromere- chromatins

Centromere- middle region of chromosome, attracts spindle fibres

Somatic cells- body cells (non-sex cells), undergo mitosis

Haploid (n)- half the genetic information (23 chromosomes)

Diploid (2n)- complete set of genetic information (46 chromosomes)

Homologous chromosomes (tetrad)- pair of chromosomes similar in shape, size, gene arrangement and gene information (not identical as they may carry different forms of the same gene)  (Example: Chromosome #1)

Synapsis- pairing of homologous chromosomes, during prophase 1 in meiosis 1

Crossing over- exchange of chromosomal segments between a pair of homologous chromosomes

Cytokinesis- division of cytoplasm (two cells produced)

 

Meiosis 1: first division, chromosome number reduced in half, synapsis and crossing over occur

Interphase 1:

  • DNA doubled (46-92)

Prophase 1:

  • each pair lines up side by side (synapsis)
  • segments of chromosomes exchanged (crossing over)
  • centrioles move to poles
  • spindle appartatus forms

Metaphase 1:

  • pairs of homologous chromosomes line up along the equator (middle of cell)
  • spindle fibres attach to centromere of each homologous chromosome (where centromeres end up is random)

Anaphase 1:

  • homologous chromosomes separate
  • move to opposite poles (segregation)
  • one chromosome (two chromatids) move to pole, now haploid
  • errors likely to occur here as chromosomes divide into new cells

Telophase 1:

  • chromosomes begin to uncoil
  • spindle fibres disappear
  • cytokinesis takes place
  • nuclear membrane forms around each group of chromosomes
  • diploid cells (46 chromosomes)

 

Meiosis 2: second division, no replication of genetic material, 4 haploid cells produced at the end, all are genetically different

Prophase 2:

  • nuclear membrane disappears
  • centriole pairs move to opposite ends
  • spindle fibres reform
  • chromosomes condense

Metaphase 2:

  • sister chromatids attach to spindle fibres in middle of the cell

Anaphase 2:

  • sister chromatids are pulled apart to opposite sides of the cell
  • errors likely to occur here as chromosomes divide into new cells

Telophase 2:

  • nuclear membrane reforms around sister chromatids
  • centriole pairs disappear
  • DNA uncoils
  • cytokinesis occurs

Gamates:

  • production of egg and sperm cells (4 egg, 1 sperm)
  • haploid= 23 chromosomes
  • daughter cells are not identical to parent cell

 

Importance of Meiosis:

  • crossing over and independent assortment give rise to genetic variation within individuals
  • independent assortment: where chromosomes end up when they split and go to the poles, different genes go both ways (occurs in Anaphase 1 and 2)
  • crossing over: genetic material is mixed with that of the other in the homologous pair, creates a mix of genes when new cells are formed (occurs in prophase 1)
  • most gamete cells receive mix of paternal and maternal chromosomes

 

Gametogenesis:

  • production that creating a sperm or egg
  • differs greatly between spermatogenesis and oogenesis
  • spermatogenesis: converts the spermatocyte into four sprematids
  • oogenesis: asymmetric cell divison produces one large cell and three small ones that degenerate into three polar bodies
  • during birth, eggs are produced until prophase 1, meiosis will continue for one cell each month beginning at puberty, final stage of meiosis 2 is not completed unless fertilized
  • when meiosis 2 is completed, the mature egg (n) has been fused with a sperm cell (n) to create a diploid (2n) zygote

 

Abnormal Meiosis: Nondisjunction:

  • occurs when two homologous chromosomes move to the same pole during meiosis 1
  • results in one of the daughter cells having an extra chromosome, while the other is missing one
  • cells do not function properly
  • can also occur in any cell if chromatids do not separate
  • three of one chromosome: trisomy
  • one less chromosome: monosomy

 

Chromosomal disorders:

Down syndrome: Extra chromosome 21

  • intellectually disabled
  • heart defects
  • physical abnormalities

Klinefelter syndrome: Extra X chromosome

  • occurs in males (extra female chromosome)
  • tall and slim
  • few pubic hair, facial hair and underarm hair

Turner Syndrome: missing X chromosome

  • occurs in females
  • short stature
  • sterile
  • lack of ovarian development
  • poor breast development
  • no menstruation

*Disorders affecting autosomes have the greatest affect on a person’s health as they impact genetic info and behaviour.

*XX= Female, XY= Male

 

 

 

 

Vocabulary: Chapter 5:

Alleles: two or more variations of a gene, alleles are located at the same position on a pair of homologous chromosomes

Dominant: alleles of this type determine the expression of the genetic trait (capital letter)

Recessive: alleles of this type are “masked” by dominant alleles (lower case letters)

Phenotype: the observable trait of an organism (eg. hair and eye colour)

Genotype: the alleles that make-up a gene (specific trait) (eg. AA, Aa, aa)

Homozygous: a genotype in which the allele pairs are the same (eg. AA or aa)

Heterozygous: a genotype that includes a dominant and a recessive allele (eg. Aa)

 

Mendelian Genetics:

Mendel’s Law of Heredity

  1. Each parent contributes one allele during cross-fertilization.
  2. Dominant allele is always expressed when the recessive allele is present.
  3. Each pair of alleles segregates during formation of sex cells.

 

Hybrid: the offsprings from two pure lines, often heterozygous

Monohybrid Cross: cross where one trait is observed

Dihybrid Cross: a cross where 2 traits are observed

 

Monohybrid Crosses: (2×2 Punnett Square)

-Does it with one trait at a time.

-Demonstrates how dominance and recessive genes could be passed onto from one generation to another.

P1 Generation: BB bb

F1 Generation: Bb Bb Bb Bb

F2 Generation: BB Bb Bb bb

**F2 Generations will always have 3:1 ratio of dominance and recessive

 

Dihybrid Crosses: (4×4 Punnett Square)

-Demonstrates Mendel’s law of independent assortment that the inheritance of one trait doesn’t dictated the inheritance of another

-In Dihybrid crossing, 2 traits are put to the test

Solving: Distributive property both genotypes

*9:3:3:1 Ratio for two heterozygous

 

 

 

Test Cross:

  • use when the genotype of 1 parent is unknown but they express a dominant phenotype
  • parent is crossed with a homozygous recessive parent
  • determining whether or not the parent is homozygous dominant or heterozygous
  • two cases for monohybrid
  • four cases for dihybrid

 

Incomplete Dominance:

  • not all alleles are fully dominant or recessive
  • heterozygous genotype can show an intermediate phenotype (blending of alleles to produce a new phenotype)
  • occurs when two alleles are equally dominant, produce a new heterozygous genotype
  • example: red dragon + white dragon = pink dragon

 

Codominance:

  • occurs when both alleles are fully expressed
  • one allele does not mask the other
  • example: red bull + white cow = roan calf (mix of white and red hair that appears in patches)

 

Lethal Alleles:

  • alleles that have a detrimental effect on the organism
  • if lethal gene is dominant and expressed immediately, organism would die, eliminate gene from population
  • if organism lives long enough to reproduce, gene is passed on to next generation

 

 

 

 

 

 

 

 

ABO Blood Group:

  • system shows both multiple allelism and co-dominance, more than two alleles possible for a given name

 

Genotype Phenotype
IAIA or IAi -dominant Type A
IBIB or IBi –dominant Type B
IAIB – dominant Type AB
ii –recessive Type O

 

Sex-linked Inheritance:

  • traits controlled by genes on either the X or Y chromosome are called sec-linked traits
  • they are identified by their different rate of appearance between the genders
  • most X-linked traits are recessive, affected male passes the allele onto daughter
  • females must inherit both alleles to be affected while males only need one
  • only females can be carriers
  • example: CVD- colour vision deficiency, hemophelia