Unit 5

Haploid vs Diploid Mitosis creates Diploid cells, which are cells that contain two complete sets of chromosomes. We abbreviate this 2n.

Haploid vs Diploid In a Haploid cell, only ONE complete set of chromosomes is present. We abbreviate it n.

Meiosis Meiosis is sexual reproduction. Only occurs in the sex organs – ovaries and testes. Results in the production of gametes, which are sex cells. Meiosis begins with a diploid cell, and the end result is 4 haploid cells. Meiosis is similar to Mitosis because there is still Interphase and PMAT, but in Meiosis, PMAT occurs twice.

Stages of Meiosis Interphase MEIOSIS I Prophase I The DNA replicates MEIOSIS I Prophase I Spindle fibers form and the chromosomes pair up. These paired chromosomes are called Homologous Chromosomes. While the Homologous Chromosomes are paired up, crossing over occurs.

Crossing Over During crossing over, genetic information (DNA) is exchanged. The result is chromatids that are no longer identical.

Meiosis I Metaphase I The homologous chromosomes line up in the cell. Anaphase I The chromosomes pull apart.

Meiosis I Telophase I The cells begin to divide into 2 cells. Cytokinesis 2 individual, haploid cells are created.

Meiosis II Prophase II Chromosomes form, spindle fibers form Metaphase II Chromosomes line up

Meiosis II Anaphpase II Sister chromatids pull apart Telophase II The 2 cells are now dividing into 4

Meiosis II Cytokinesis 4 haploid cells are formed. All are genetically different.

Stages of Meiosis Gamete formation in males Gamete formation in females

Meiosis Video https://www.youtube.com/watch?v=toWK0fIyFlY

Genetic Variation How do we each become our own individual with our own unique set of genes? How does genetic variation occur? Genetic variation occurs during crossing over (Prophase I)

Genetic Variation cont. Occurs during random assortment of chromosomes during the different stages of meiosis. This is the Law of Independent Assortment.

Genetic Variation Law of Segregation – during meiosis, the chromosome splits and the chromatids segregate. Each gamete gets half of the genetic information.

Genetic Variation cont. Occurs during fertilization – ½ of DNA comes from each parent Gene mutation Non-disjunction – chromosomes did not properly split

Karyotype A karyotype is a picture or profile of a person’s chromosomes. Chromosomes are paired up and numbered 1-22, and the 23rd chromosome is labeled XY and determines gender. We use karyotypes to show chromosomal abnormalities.

What can you notice about this Karyotype – what is it missing? On the X and Y chromosomes, there is only 1 X chromosome. It is missing a second sex chromosome. This is called Turner’s Syndrome.

More practice with karyotypes Open your textbook to…Pg. 318 Chromosomes for Male ? Female? Pg. 329 Male of Female? Normal or not? Pg. 335 Male or Female?

This is a Karyotype for Trisomy 21. Notice there are 3 chromosomes on the 21st chromosome. This was caused by a non-disjunction. Trisomy 21 is also known as Down Syndrome.

Gregor Mendel Father of genetics Austrian Monk He did experiments on Pea plants to show how traits were passed down He studied the shape, seed color, outer coat, pea pod, and stem to see which traits occurred more or less often. He was the first to observe: The Law of Independent Assortment The Law of Segregation

Genotype Phenotype The genes of the organism What the organism looks like

Allele – one or more versions of a gene. Located at a specific position on a specific chromosome Dominant Allele What will be expressed. It “masks” other alleles. Written in upper case. Recessive Allele It will only be expressed if the dominant allele is not present. Written in lowercase.

Heterozygous Hybrid Having 2 different alleles for a gene Homozygous Same; purebred Have 2 of the same alleles for a gene

Punnett Squares The diagram used to predict the genotype and phenotype. As a class do the Simpson’s genetics lab. Academic complete #1-4. Honors start @ #4.

Punnett Squares B BB Bb b Bb bb Ex. You have 2 mice that are heterozygous for their brown coats. Brown is the dominant color and white is the recessive. Create a Punnett Square that shows the cross between these two mice. B b B BB Bb b Bb bb What are the ratios of genotypes you will get? 1:2:1 What percent of each phenotype will you see? 75% brown 25% white Simpson’s Genetics worksheet. Academic do #1-4. Honors do #4 - ___

Incomplete Dominance Punnett Square

Incomplete Dominance When one allele is not completely dominant over the other. The heterozygous genotype will result in a blend. Ex. Snapdragons

Co-dominance Co-dominance results in the expression of both traits. Baby lab hair type through skin tone

Polygenic Traits Traits which are coded for by more than one allele. Usually results in blending of traits. Ex. Hair color, eye color, skin color

Blood Types Blood types are an example of codominance. A and B are both dominant. O is recessive.

Sex-Linked Traits Trait is more likely to be inherited by males. Recessive Genes for these traits are found on the X and not the Y chromosome. This is why the X is bigger than the Y.

Sex-Linked Traits

Examples of Sex-linked Traits Red/Green Colorblindness Hemophilia – the inability of the blood to properly clot Show Ameoba sisters video on sex-linked traits: https://www.youtube.com/watch?v=h2xufrHWG3E

Pedigrees Charts are made to show how traits are passed down through the generations. Things to note: Generations are denoted by Roman numerals. Number individuals from left to right.

Pedigrees Symbols: Female Male Married Divorced Deceased Affected Male Siblings

Hemophilia in the Royal Family

Bellwork From Genetics practice problems, finish the page on Blood Type Punnett Squares Finish reading and answering questions on blood types

What else can Punnett Squares be used for? Punnett Squares can also be used to show how genetic disorders get passed down from parent to offspring. PKU is a recessive gene. Ex. Phenylketonuria (PKU) A genetic disorder that causes the build up of the amino acid phenylalanine in the body. Symptoms: delayed development Intellectual disability P p Behavioral, emotional and social problems Psychiatric disorders P PP Pp Neurological problems that may include seizures Hyperactivity Poor bone strength p Pp pp Skin rashes (eczema)

Genetic Disorders Cystic Fibrosis Most commonly caused by a deletion of 3 base pairs on the 7th chromosome. Approx. 2500 babies are born each year in US with Cystic Fibrosis. It is estimated that 10 million Americans are carriers of the gene. Recessive Symptoms: Respiratory problems Mucous in the lining of the lungs

Genetic Disorders Huntington’s Disease Dominant Trait Caused by a mutation on the 4th chromosome Approx. 1 in 30,000 people in US have Huntington’s Symptoms: Affects thinking, motion, and movement Symptoms do not usually appear until age 30-50

Genetic Disorder Chart Recessive, Dominant, or Chromosome Affected Symptoms/Traits