Chapter 6 &7 Meiosis and Sexual Reproductions PDF

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These notes cover Week 4 Life Science notes in Chapters 6 and 7: Meiosis and Sexual Reproduction....

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Chapter 6 &7: Meiosis and Sexual Reproductions ❖ Gene= A sequence of DNA Note: -

Genes provide instructions for making proteins.

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Two copies of each chromosome (and each gene) in diploid organisms.

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Homologous chromosomes are one from each parent passed to offspring.

❖ Humans are diploid organisms -

Have two copies of genes found on homologous chromosomes

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Have some function but DNA sequence may differ

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MAy have two different alleles of the same gene

Remember: Males is XY, Females is XX ❖ Genotype: Is the particular genetic or allele makeup of an individual (Your genetic makeup). Examples: F=Blue eyes; f=green eyes -

FF=Blue eyed dominant

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FF=Blue eyed dominant

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Ff=green-eyed recessive

❖ Phenotype: Is the observable or measurable features of an individual (What you look like). Examples: Blue eyes+ brown hair or brown hair+green eyes or Black hair and Blue eyes Sexual Reproduction ❖ Is the combination of maternal (mother) and paternal (father) -

Are joined together during fertilization

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Determines the genotype and contributes to the phenotype

❖ Requires special sex cells: sperm, egg -

Sperm comes from Males

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Eggs come from Females

❖ Gametes: Are reproductive cells that carry one copy of each chromosome Ex: Haploid ❖ Meiosis: Is the special cell division needed to reduce from diploid to haploid -

Meiosis generates genetically unique haploid gametes.

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Haploid sperm fertilizes a haploid egg resulting in a diploid zygote.

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Zygotes divide by mitosis into an embryo. Meiosis (two separate divisions)

Meiosis I ➢ Separates homologous chromosomes ➢ Each daughter cell is haploid ➢ Each chromosome still has 2 sister chromatids Meiosis II ➢ Separates sister chromatids ➢ 4 haploid daughter cells are created ➢ Develop into egg or sperm Meiosis and Genetic Diversity ➢ No 2 gametes are Identical due to Recombination and Independent Assortment. ➢ Recombination: When maternal and paternal chromosomes pair and physically exchange DNA segments.

➢ Independent Assortment: Are alleles of different genes are distributed independently of one another. Examples: capital=dominant and lowercase=recessive A=blue eyes D=black hair E=brown eyes d=brown hair e=brown eyes ADe= Blue eyes, black hair, and brown eyes aDE=black hair and brown eyes ade=brown hair and brown eyes Disorders in Chromosome Number ❖ Nondisjunction: Homologous chromosomes fail to separate in Meiosis I or sister chromatids don’t separate in Meiosis II. ❖ Monosomy; fetal development fails (except single X, Turner Syndrome) ❖ Trisomy (extra chromosome) can survive (13,15,18,21,, or 22) 21 Down Syndrome ❖ XXY Kleinfeller syndrome ❖ XO Turner Syndrome ❖ If an egg cell with an extra X chromosome (XX) is fertilized by a sperm cell with one Y chromosome, the resulting child will have Kleinfelter syndrome Key Words

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Down syndrome= Trisonomy 21

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Edward’s syndrome= Trisonomy 18

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Patau syndrome=Trisonomy 13

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Cri du chat- syndrome= 5p minus syndrome (partial deletion of the short arm of chromosome 5)

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Wolf-Hirschhorn syndrome= Deletion 4p syndrome

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Jacobsen syndrome= 11q Deletion disorder

The Inheritance of Traits ❖ The Human life cycle: Growth and reproduction of an individual ❖ Adults produce gametes by meiosis ❖ Gametes (sperm and egg) fuse during fertilization to form single-celled zygotes ❖ Continued cell divisions form the embryo ❖ Genes: Segments of DNA that code for proteins -

Prokaryotes- single, circular chromosomes

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Eukaryotes-linear chromosomes

Remember: Human cells have 46 chromosomes. Different Alleles ^ Mistakes in copying DNA (mutations) produce different versions of genes. ❖ Homologous pairs: Are equivalent chromosomes; pairs contain one chromosome received from each parent. Note: The parent cell has two complete copies of the manual. Unique Offspring ❖ Segregation in Meiosis: homologous chromosomes separate from each other into

different gametes. -

Gamete gets just one copy of each page manual.

❖ Independent Assortment: Homologous move into gametes, randomly and independently of other chromosomes. -

Due to random alignment during Metaphase I

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Due to Independent Assortment, the instructions in one sperm cell are a unique combination of pages.

Genetic Diversity ➢ About 8 million different combinations of chromosomes are possible. Note: Random Fertilization produces more diversity: 8 mil x 8 mil=64 trillion possibilities Genotype: recessive and Dominant ❖ Heterozygous: two different alleles (Aa) ❖ Homozygous: two identical alleles -

Homozygous dominant (AA)

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Homozygous recessive (aa)

❖ Punnett Square: A diagram to determine the probabilities of offspring having particular genotypes. -

Based on the genotype of parents

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Matches up all possible gametes

For example:

➢ Father is tall and the mother is tall. ➢ But, both parents have a recessive allele for being short. ➢ Hence why both parents have the alleles Tt. ➢ There is a 25% chance that their child comes out short and a 75% chance that the child comes out TALL. Cystic Fibrosis ❖ It is a genetic disease. ❖ Caused by a single gene mutation -

Changes in the nucleotide sequence of DNA

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Creates a new mutant allele

❖ The allele of the CTFR gene Cystic Fibrosis transmembrane regulator gene ❖ During Cystic Fibrosis, your lungs are clogged up with mucus. ❖ Cystic Fibrosis is most common in European descent. ❖ CFTR moves ions in and out of cells ❖ People with normal phenotypes can still pass CF alleles to offspring. ❖ People with CF alleles can have children that do not come out with the disease.

Note: Cystic Fibrosis (CF) is caused by a recessive allele. -

An allele that affects phenotype only of the organism has two copies of that allele

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Hidden by a normal or DOMINANT allele

Remember: recessive alleles are lower-cased (aa)(a) and DOMINANT alleles are upper-cased (AA)(A) ❖ Huntington’s disease is a DOMINANT human genetic disease....