UNIT VII – MEIOSIS & 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 ________. I.SEXUAL REPRODUCTION & MEIOSIS In ______ ___________, an egg and sperm cell fuse together to create a fertilized egg or _______. Egg and sperm cells are known as _________. Aka: ________ Gametes are the only cells in the body that are NOT produced by ________. Instead gametes are created through a special process of cell division called _________ which _______ the chromosome number. Meiosis only occurs in the ________ of females and the _____ of males. heredity our parents genetics sexual reproduction ZYGOTE GAMETES mitosis MEIOSIShalves Sex cells ovariestestes

A. Chromosome Number 1.Human ________ cells, or body cells, contain ____ chromosomes. Somatic cells are _______ (__) because these cells contain a ______ set of chromosomes: o Half (23) from _____ (________) & half (23) from _____. Aka: (________) “Matching” chromosomes are known as _____________ ______. o A homologous pair is a pair of chromosomes – one from each parent with the same __________________ or _______. 2.Human gametes (____ & ______) contain ____ chromosomes. They are _________ (___). These cells contain _____ the total number of chromosomes, a ______ set of chromosomes. When the gametes fuse together during ______________, the resulting ________ has ____ chromosomes. SOMATIC46 DIPLOID2n double mom dad HOMOLOGOUS PAIRS type of information genes eggsperm 23 HAPLOIDn half single FERTILIZATION ZYGOTE46 maternal paternal

Phases of Meiosis 46 chromosomes (2n) 23 chromosomes (n) 46 chromosomes (2n) 23 chromosomes (n)

B. Crossing Over 1.Occurs during meiosis when _____________ pairs of chromosomes come together. 2.A portion of one _____ __________ may be broken off and exchanged with the corresponding portion of a sister chromatid of the homologous chromosome. 3.Crossing over is very common and _________ the genetic __________in offspring. HOMOLOGOUS sister chromatid increasesvariability

B.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. 1.Individual units called _______ determine inheritable characteristics. A gene is a portion of _____ that codes for a specific ______. Different forms or possibilities for a gene are called ________. For example, the alleles for the gene for plant height are ______ and _______. II.HISTORY OF GENETICS A.Gregor Mendel – Known as the “Father of _________”. 1.Famous for his experiments with ____ plants. 2.Mendel studied seven ______, including plant: height, seed color, flower color, etc. 3.A trait is an ________ ____________. Genetics pea inherited characteristic TRAITS GENES DNATRAIT ALLELES tall short

2.For each gene, an organism inherits ____ alleles, one from each _______. a.If the two alleles are the same, the organism is said to be ____________ for that trait and the allele will be expressed. b.If the two alleles differ, the organism is said to be _____________ for that trait and ONLY one allele will be expressed. c.The expressed allele is the __________ allele. It is designated by an ______- case letter. d.The allele that is not expressed in a heterozygous trait is considered ________ and it is designated by a ______-case letter. e.A recessive allele is ONLY expressed when an organism is ___________ for that allele. t f.For example: If tall plants are dominant then it would be represented as T making short plants recessive & would be written as t. two parent homozygous heterozygous dominant upper recessivelower homozygous WHAT IS HOMOZYGOUS? WHAT IS HETEROZYGOUS? Dominant Dominant Recessive

3.In meiosis, the two alleles for a trait segregate (________) 4.Each egg or sperm cell receives a copy of one of the two alleles present in the somatic cells of the organism. 5.Due to the random separation of chromosomes in meiosis, there is a ______ chance that a copy of that allele will end up in the gamete produced. This is known as the _____________________. D.Genetics Terminology 1.Phenotype - ________ description of trait. Example:____, _____; _____ ____. 2._________ – genetic make-up of an organism or set of alleles. Example: ____, _____, OR _____ separate 50% principle of segregation physical tallshort eye color Genotype TT tt Tt Genotype: Homozygous recessive (bb) Genotype: Homozygous Dominant (BB) OR Heterozygous (Bb)

3. Application of Terminology If round pea seeds are dominant to wrinkled pea seeds, what letter would represent round vs. wrinkled? Round is designated __ Wrinkled is designated __. a. Homozygous dominant for pea seed shape is written ___. Genotype = ___; Phenotype = ________ b. Heterozygous for pea seed shape is written __. Genotype = ___; Phenotype = _______. c. Homozygous recessive for pea seed shape is written ___. Genotype = ___; Seed shape? _________ III. ANALYZING INHERITANCE A. Probability 1.Due to the law of segregation, if you know the _________ of the parents, you can predict the likelihood of a trait occurring in the offspring. Probability can be written 3 ways. 2.The probability of a coin coming up heads after being flipped is (percent) ____, (ratio) _____, or (fraction) ___. R r RR RR Round Rr Rr Round rr rrWrinkled genotype 50% 1:2 1/2

B. Punnett Squares 1.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. 2.How to Solve a Punnet Square 1. Determine the genotypes (letters) of the parents. 2. Set up the Punnet square with one parent on each side. 3. Fill out the Punnet square middle 4. Analyze the number of offspring of each type. Example: In pea plants, round seeds are dominant = ___ to wrinkled = ____ Determine the possible offspring if both parents are heterozygous = **If you get stuck make a "key". Sometimes the problems won't give you obvious information. meiosisfertilization (R) (r) (Rr) Phenotype: 75% Round 25% Wrinkled Genotype Genotype: 25% RR (homozygous dominant) 50% Rr (heterozygous) 25% rr (homozygous recessive)