Unit 8 Meiosis and Mendel Genetics and Inheritance

UNIT 7 - INTRODUCTION TO GENETICS Although the resemblance between generations of organisms had been noted for thousands of years, it wasn’t until the 1800s that scientific studies were carried out to develop an explanation for this. Today we know that we resemble our parents because of _______________, which is the set of characteristics we receive from ______________________. The study of heredity is known as _________________. heredity our parents genetics

I. SEXUAL REPRODUCTION & MEIOSIS (pp ) In sexual reproduction, an egg and sperm cell fuse together to create a fertilized egg or _______________. zygote

A. Chromosome Number 1. Somatic Cells - _____________ cells  Human somatic cells contain ________ chromosomes  ______________ or ________ meaning they contain a ____________ set of chromosomes, half ( _____ ) from _________ and half from ________.  “Matching” chromosomes are known as __________________________________________. A homologous pair is made up of a copy of a chromosome from each parent, with the same ___________. Body 46 Diploid 2n double23 Dad Mom Homologous pairs genes

Homologous Chromosomes

GAMETES 2. Gametes - ___________ and _______________ cells also defined as sex cells.  Human gametes contain ______ chromosomes.  ______________ or ______ meaning there is _____ set of instructions for each ______.  When gametes fuse together in _____________________, the ________________ produced is _____________ and has _______ chromosomes. EggSperm 23 Haploid n one gene fertilization zygote diploid 46

B. Meiosis  Special type of cell division that only occurs in specialized germ cells in _______________ of females and ______________ of males.  In meiosis, DNA is replicated once but cell divides ___________, resulting in ______ cells with _______ the original chromosome number. ovaries testes 2X, two times 4 1/2

MEIOSIS  In females, process is known as ________________________.  In males, process is known as _________________________.  In both males & females, prior to meiosis I, DNA is replicated during ______ of ________________________. oogenesis spermatogenesis S interphase

 Meiosis occurs in two stages:

1. Meiosis I Prophase I  Unlike prophase of mitosis, ___________________________ come together to form a ______________.  Tetrads are held together at the ___________________. Homologous pairs tetrad centromeres

Meiosis I  Crossing Over  Exchange of genetic information between a ________________________________ with its ___________________________________.  Occurs very frequently  Allows for __________________________. Sister chromatid Non-sister homologue Genetic variation

Meiosis I Metaphase I  _____________________________ align in equator of cell  Each homologue consists of _______________________________________. Anaphase I  __________________________________________ are pulled apart  _________________, _________________________ still intact Tetrads Two sister chromatids Homologous pairs CentromeresSister chromatids

Meiosis I Telophase I  Two cells are formed, each with _______ chromosomes  Each chromosome still composed of two ___________________  Two cells produced at the end of meiosis I are _______________ because______________________ 23 Sister chromatids haploid There are no homologous pairs present

MEIOSIS II

2. Meiosis II Continues with the two cells formed moving directly into prophase II without any further _____________________ of DNA. In anaphase II, ______________________ are pulled apart. Two new cells are formed from each of the two cells formed in meiosis I, resulting in a total of ___________ new cells, each with ____________the original number of chromosomes. Cells produced are called ____________________. replication Sister chromatids 4 1/2 Gametes

II. HISTORY OF GENETICS (pp ) A. Gregor Mendel  Known as the “Father of _______________”  Famous for his experiments with ________ plants. Genetics pea

Mendel  Used true-breeding pea plants, which means ________________________; characteristics always show. Known as the ____________ generation.  Studied seven ______________, including plant height, seed color, flower color, etc. o A trait is an ________________________________. pureline, purebred P traits Inherited characteristic

Mendel  Pea plants cross-pollinate, meaning pollen from one plant fertilizes an egg from another, but they can also self-pollinate, meaning pollen can fertilize egg from ______________ plant. Mendel controlled the fertilization process of the pea plants by preventing __________________________________ and controlling ___________________________________. same Self-pollination Cross-pollination

Pea Traits Studied

B. Mendel’s Results  P generation – Crossed __________________ plants with one trait with ________________ plants with the other.  For example, _____________________________________________  F 1 generation – Offspring produced from _________________. In F 1, one trait ____________. For example, tall plants X short plants = __________________________.  F 2 generation – Offspring produced from _________________. In F 2, trait that disappeared in F 1 reappeared in __________ of the offspring; the other ¾ showed _____________________________. True-breeding TT (tall) x tt (short) P X P disappeared All tall plants F1 X F1 1/4 Dominant trait

Mendel’s Principles C. Mendel’s Principles – After analyzing his results carefully, Mendel formed conclusions that increased understanding of inheritance and opened the door for the study of genetics.  Individual units called ___________ determine inheritable characteristics. A gene is a portion of ___________ that codes for a specific ____________. genes DNA trait

Alleles and Genes

Mendel’s Principles  For each gene, an organism inherits two alleles, one from each __________________. Alleles are different forms or ____________________ of a ___________. For any given trait, o If an organism is ___________________, its alleles are the same and the trait will be expressed. o If the alleles differ, the organism is said to be ___________________ for that trait and only one allele will be expressed. The expressed allele is the ______________ allele, designated by an __________-case letter. The allele that is not expressed in a heterozygous trait is _________________, designated by a _____________-case letter. A recessive allele is only expressed when an organism is ________________. parent versions gene homozygous heterozygous dominant upper recessive lower homozygous

Mendel’s Principles  Principle of Segregation - In meiosis, the two alleles for a trait segregate (_______________). Each egg or sperm cell receives a copy of one of the two alleles present in the somatic cells of the organism. There is a _________ chance that a copy of that allele will end up in the gamete produced.  Principle of Independent Assortment – The way one pair of alleles segregates has no influence on any other pair of alleles. separate 50%

Independent Assortment

D. Genetics Terminology 1. Phenotype - ________________ description of trait; for example, ______________ 2. Genotype – Genetic make-up of an organism or set of alleles; for example, ____________________. Physical Tall, short TT, Tt, heterozygous, etc..

Genetics Terminology 3. Application of Terminology - If round pea seeds are dominant to wrinkled pea seeds, round is designated _____ and wrinkled is designated ______. a. Homozygous dominant Genotype = ________; Phenotype = ________ b. Heterozygous Genotype = ________; Phenotype = ________ c. Homozygous recessive Genotype = ________; Phenotype = ________ R r RRround Rr round rr wrinkled

III. ANALYZING INHERITANCE (pp ) A. Probability Due to the law of_______________, if you know the genotype of the parents, you can predict the likelihood of a trait occurring in the offspring. Probability can be written 3 ways. The probability of a coin coming up heads after being flipped is (fraction) _____, (ratio) ________, or (percent) _______. segregation 1/2 1:2 50%

B. Punnett Squares A Punnett square is a tool used to predict the possible outcomes of _______________ and ____________________; in other words, a Punnett square is used to determine the probability of certain traits appearing in offspring. meiosis fertilization

Punnett Practice A-D Must have a key And Cross with Each problem For full credit

Incomplete Dominance Neither allele has “complete” dominance over the other; heterozygous phenotype is a blend of the 2 homozygous phenotypes Ex: snapdragons R = red W = white RW = pink

Codominance Codominance – Both alleles share dominance and are always expressed if present. Ex: In chicken B = black feathers W = white feathers BW = black AND white feathers X

Polygenic Traits “Many genes” ; Many traits are controlled by more than one gene; have a variety of choices for expression. Ex: _hair color, eye color, skin tone

Multiple Alleles Many genes that have more than 2 alleles, although an individual only has 2 alleles for the gene. Ex: blood group. There are 3 possible alleles for this gene.