SBI3U Final Exam Review : Unit 2 - Genetic Continuity

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82 Terms

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Diploid

A cell that contains pairs of homologous chromosomes, represented by 2n

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Haploid

A cell that contains half the number of chromosomes as the parent cell, represented by n

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Selective Breeding

The process by which humans use animal and plant breeding to develop particular phenotypic traits by choosing which males and females will sexually reproduce

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Crossing Over

The exchange of chromosomal segments between a pair of homologous chromosomes at a chiasma during prophase I

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Nondisjunction

The failure of homologous chromosome pairs or sister chromatids to separate during the anaphase stages in meiosis

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Mitosis

The stage of the cell cycle where a cell’s nucleus and genetic material divide

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Phases of Mitosis

Interphase occurs before mitosis to replicate the chromosomes.

Prophase

Metaphase

Anaphase

Telophase

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Interphase

The stage of the cell cycle during which a cell carries out its normal functions, grows, and makes copies of its genetic material in preparation for the next stage of the cycle. The cell grows, matures, copies its DNA, and prepares for division

Growth 1 is the major period of growth where the cell synthesizes many new molecules

Synthesis is the period where DNA is replicated as uncondensed fibres called chromatin

Growth 2 involves the production of more molecules

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Prophase

The stage where the cell’s chromatin condenses into chromosomes, the nucleus and nucleolus disappear, and spindle fibres form from the centrosomes and move towards the poles

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Chromosome

A structure in the nucleus that contains DNA

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Sister Chromatid

One of two chromosomes that are genetically identical and held together at the centromere

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Centromere

The region where two sister chromatids are held together in a chromosome

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Spindle Fibre

A microtubule structure that facilitates the movement of chromosomes within a cell

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Centrosome

A structure that helps to form the spindle fibres

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Metaphase

The stage where the spindle fibres from each pole attach to the centromere and guide the chromosome to the equator of the cell

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Anaphase

The stage where each centromere splits apart, and sister chromatids, now individual chromosomes, are separated to opposite poles so that each pole has a complete set of DNA

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Telophase

The stage that begins when chromosomes reach the opposite ends of the cell, where chromosomes start to unwind, spindle fibres break down, and the nucleus and nucleolus reform

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Cytokinesis

The stage of the cell cycle that involves the division of the cell cytoplasm and creation of two new daughter cells

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Meiosis

The cellular process that produces cells containing half the number of chromosomes as the parent cell (genetic reduction) and are genetically unique through combinations of alleles (genetic recombination)

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Interphase Before Meiosis

Cells that will divide by meiosis will proceed through growth and synthesis, and replicate their chromosomes, so that the meiosis begins with duplicated chromosomes

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Phases of Meiosis

Interphase happens before meiosis

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Prophase I

Each pair of homologous chromosomes condense and line up side by side in synapsis, where genetic information is exchanged through crossing over. This is the longest meiotic phase

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Tetrad

Two chromosomes, or four chromatids

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Chiasma

The site where chromosomes cross over

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Metaphase I

The pairs of homologous chromosomes (tetrads) line up along the equator of the cell, and spindle fibres attach to the centromere of each homologous chromosome. This is the shortest meiotic phase

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Anaphase I

The homologous chromosomes separate and move to opposite poles, which turns a diploid cell into a haploid cell. Sister chromatid remain attached

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Telophase I

Homologous chromosomes begin to uncoil and the spindle fibres disappear, the nuclear membrane forms, and two haploid cells form through cytokinesis

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Prophase II

The nuclear membrane disappears and spindle fibres reappear

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Metaphase II

A haploid number of chromosomes line up at the equator

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Anaphase II

Sister chromatids are pulled apart at the centromere by the spindle fibres towards opposite poles of the cells

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Telophase II

The nuclear membrane and nuclei reform

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Cytokinesis After Meiosis

The two cells that have undergone telophase II split once more to form four unique haploid cells

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Significance of mitosis

It allows cells to grow, repair, and replace other cells.

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Significance of meiosis

It forms genetically distinct haploids through genetic recombination (independent assortment, random selection, and crossing over). The genetic uniqueness allows populations to have a greater variety in genes. The haploid cells allow two breeding individuals to form a diploid zygote, allowing for greater genetic diversity through sexual reproduction.

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Independent Assortment

The orientation of each chromosome in a homologous pair to one pole, which can result in a variation of possible gametes containing a combination of maternal and paternal chromosomes

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Monohybrid Cross

A cross of two individuals that differ by one trait

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Mendelian Ratio

An approximate ratio of 3:1 dominant to recessive phenotypes in a monohybrid cross between two heterozygous parents

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Dihybrid Cross

A cross of two individuals that differ in two traits due to two different genes

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Steps of solving a dihybrid cross

Write a legend of each present allele

Write and box the parent line (the cross of each genotype)

Illustrate, with arrows, the possible gametes produced by each parent

Create a Punnett Square with the gametes of one parent along the top, and the gametes of the other along the side. The cross of each goes in the boxes.

Express the genotypes and phenotypes through ratios, fractions, or percents

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Genotype ratios of a dihybrid cross between two heterozygotes

1 AABB

2 AABb

2 AaBB

4 AaBb

1 AAbb

2 Aabb

1 aaBB

2 aaBb

1 aabb

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Phenotype ratios of a dihybrid cross between two heterozygotes

9 A_B_ (dominant, dominant)

3 A_bb (dominant, recessive)

3 aaB_ (recessive, dominant)

1 aabb (recessive, recessive)

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Polygenic Traits

Traits controlled by multiple alleles

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Codominant Genes

Two different alleles at a locus are responsible for different phenotypes, and both alleles affect the phenotype of the heterozygote

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Solving dihybrid crosses with codominant genes

Solve as normal. The heterozygote of codominant alleles will express both as dominant (ex. Type AB blood is made of codominant IA and IB alleles)

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Incomplete Dominance

The phenotype of a heterozygote is an intermediate of both the dominant and recessive traits

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Solving dihybrid crosses with incomplete dominance

Solve as normal. The heterozygote will be a new phenotype (ex. in flowers, crossing a red and a white pigment allele will create a pink offspring)

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Sex-Linked Genes

A gene coded on a sex chromosome

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Solving dihybrid crosses with a dominant X-linked gene

In a monohybrid cross, the gametes come from XX and XY. Only the cross of an affected X chromosome will carry and express the gene. The phenotypes are:

  • XX - Normal female

  • XAX or XAXA - Affected female

  • XY - Normal male

  • XAY - Affected male

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Solving dihybrid crosses with a recessive X-linked gene

In a monohybrid cross, the gametes come from XX and XY. Only the cross of an affected X chromosome will carry the linked gene, but all X chromosomes must be affected to express it. The phenotypes are:

  • XX - Normal female

  • XaX - Carrier female

  • XaXa - Affected female

  • XY - Normal male

  • XaY - Affected male

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Lethal Alleles

A mutated gene that is capable of causing death

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Solving dihybrid crosses with a dominant lethal allele

Solve normally. Both heterozygotes and dominant homozygotes will die. In a cross of heterozygotes, the ratio is 1 living: 3 affected/dead.

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Solving dihybrid crosses with a recessive lethal allele

Solve normally. The homozygous lethal allele genotype will die, and the heterozygote (1 lethal, 1 normal) will express an abnormal phenotype. A cross between two heterozygotes will have a ratio of 1 dead: 2 abnormal: 1 normal

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Complementary Genes

Genes can only be expressed in the presence of other genes

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Solving dihybrid crosses with complementary genes

Solve normally. If a trait requires two different alleles to be dominant to be expressed, A_bb would be the recessive phenotype, aaB_ would be the recessive phenotype, and A_B_ would be the dominant phenotype. The ratio for a cross of two completely heterozygous parents is 9:7 for dominant to recessive.

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Epistasis

One gene masks the expression of a different gene for a different trait

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Solving dihybrid crosses with epistasis

Solve normally. If the genotype bb masks a gene, A_bb would not show the A trait, aaB_ would show the recessive phenotype for gene A, and A_B_ would show the dominant phenotype for A

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Antigen/Agglutinogen

The proteins on the surface of a red blood cell that indicates the blood type.

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Antibodies/Agglutinin

Proteins in the blood that can attack specific antigens, causing agglutination and hemolysis, which limits compatibility

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Blood type compatibility

Blood types cannot receive blood with antigens that it has antibodies against

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Genotype of type A blood

IAIA or IAi

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Genotype of type B blood

IBIB or IBi

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Genotype of type AB blood

IAIB

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Genotype of type O blood

ii

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Rh Factor

A type of antigen on blood cells, indicated by a + or -

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Genotype for Rh+ blood

RR or Rr

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Genotype for Rh- blood

rr

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Hemolytic disease

An Rh- mother carries an Rh+ baby, and becomes sensitizes to the Rh+ (she produces antibodies). If the mother carries a second child with Rh+, the antibodies will attack the baby

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Type A+

Agglutinogens: A, Rh

Donates to: A+, AB+

Agglutinins: B

Receives from: A+, A-, O+, O-

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Type A-

Agglutinogens: A

Donates to: A+, A-, AB+, AB-

Agglutinins: B, Rh

Receives from: A-, O-

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Type B+

Agglutinogens: B, Rh

Donates to: B+, AB+

Agglutinins: A

Receives from: B+, B-, O+, O-

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Type B-

Agglutinogens: B

Donates to: B+, B-, AB+, AB-

Agglutinins: A, Rh

Receives from: B-, O-

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Type AB+

Agglutinogens: A, B, Rh

Donates to: AB+

Agglutinins: NONE

Receives from: A+, A-, B+, B-, AB+, AB-, O+, O- (UNIVERSAL RECEIVER)

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Type AB-

Agglutinogens: A, B

Donates to: AB+, AB-

Agglutinins: Rh

Receives from: A-, B-, AB-, O-

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Type O+

Agglutinogens: Rh

Donates to: A+, B+, AB+, O+

Agglutinins: A, B

Receives from: O+, O-

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Type O-

Agglutinogens: NONE

Donates to: A+, A-, B+, B-, AB+, AB-, O+, O- (UNIVERSAL DONOR)

Agglutinins: A, B, Rh

Receives from: O-

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Karyotype

A photograph of pairs of homologous chromosomes in a cell

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Karyotype Notation

# of chromosomes, all sex chromosomes ± the autosomal chromosome that has aneuploidy

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Monosomy

The loss of a chromosome in an autosome as a result of non-disjunction

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Trisomy

The gain of an extra chromosome in an autosome as a result of non-disjunction

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Down’s Syndrome

47, XX or XY, +21

Trisomy 21

Intellectual disabilities and short stature

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Turner Syndrome

45, XO

Short stature and sexual underdevelopment

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Klinefelter Syndrome

47, XXY

Sexual immaturity